VERGERONT, J.

On this appeal from a judgment of conviction for driving while under the influence of an intoxicant (OWI) and with a prohibited alcohol concentration (PAC), Christopher Renz raises these issues: (1) Does the statute regulating mufflers, § 347.39, Stats., violate the due process clause due to vagueness? (2) Does § 343.303, Stats., require probable cause to arrest before an officer may request a breath sample for a preliminary breath test (PBT)? (3) If probable cause to arrest is required before the administration of a PBT, was that standard met in this case? We conclude the muffler statute is not unconstitutionally vague and therefore the officer's detention of Renz for a violation of that statute was proper. We also conclude § 343.303 does require probable cause to arrest before administration of the PBT, and the officer here did not have probable cause to arrest before asking Renz to provide a breath sample. We therefore reverse the trial court's order denying Renz's suppression motion and the judgment of conviction.

BACKGROUND

Renz was arrested for OWI in violation of § 346.63(1)(a), Stats., after Deputy Sheriff David Drayna stopped him because of the loud sound of exhaust emitting from Renz's vehicle. Based on a subsequent blood test, Renz was also charged with driving with a PAC in violation of § 346.63(1)(b). Renz moved to suppress evidence on the ground that the stop was unlawful because the officer did not have a reasonable suspicion to believe that Renz's vehicle failed to comply with § 347.39, Stats. He also moved to suppress on the ground that the officer did not have probable cause to arrest at the time he requested Renz submit to a PBT, and the PBT result could therefore not be considered in assessing the existence of probable cause.

At the hearing on the motions, Officer Drayna presented the only testimony. He had been a deputy sheriff for six years and had made over 200 arrests for OWI. He was on duty in the early morning of February 12, 1996, traveling on Highway 106 in Jefferson County. Although the windows of his car were closed and his radio was on, he could hear exhaust emitting from a vehicle passing his car. Based on his Wisconsin State Patrol Academy course on equipment of motor vehicles, he concluded that the muffler on the vehicle violated § 347.39(1), Stats., which requires motor vehicles to be "equipped with an adequate muffler in constant operation and properly maintained to prevent any excessive or unusual noise. . . ." He had learned as a basic rule of thumb that if a vehicle made after 1979 was louder than a car with a muffler that had just "come from the factory," there was a violation of the statute. The vehicle was a 1991 Chevy Camaro. Drayna testified that he knew the muffler was defective and had leaks, otherwise it would not be as loud as it was. In his opinion, it was "excessively loud."

Officer Drayna pulled the vehicle over, using his emergency lights, and spoke to the driver, who identified himself as Renz. Renz stayed in his car and rolled down the window to speak to Officer Drayna. The officer detected a strong odor of intoxicants coming from the vehicle. He explained to Renz that he stopped him because of a defective exhaust, and Renz acknowledged that he knew it "had leaks and was loud." Officer Drayna returned to his car to run a routine license check, and when he went back to speak to Renz, he again noticed a strong odor of intoxicants. Officer Drayna asked Renz to step out of his car and asked him if he had been drinking that evening. Renz replied that he was a bartender at a tavern and had consumed three beers earlier in the evening. The officer did not observe Renz's speech to be slurred.

At the officer's request, Renz agreed to submit to field sobriety tests. Officer Drayna was trained to administer these tests by the National Highway Traffic Safety Administration. The first test was the alphabet test, and Renz recited the alphabet correctly. For the one-legged stand test, Renz was instructed to stand on one leg to the count of thirty, but he lost his balance at the count of eighteen and put his foot down. He started the test again, beginning with the number ten, and continuing the count to thirty. He performed all other aspects of the test correctly, including beginning with his feet together, keeping his arms down, and putting his foot of choice directly in front of him. Renz exhibited one out of four "clues" of intoxication on this test, according to the manual Officer Drayna used.

The heel-to-toe test involved walking heel to toe on an imaginary line nine steps in one direction, turning, and walking nine steps back. Renz left a gap of about one-half inch to an inch between steps. He lost his balance on the return set of nine steps, meaning that he stepped off the imaginary line on step seven, then restarted and finished the test. Renz appeared to the officer to be unsteady while performing this test, meaning that he swayed from left to right. Renz did take the correct number of steps; make a proper turn; did not lose his balance during the instructions; did not start walking too soon; did not stop while walking; and did not raise his arms from his sides while walking. According to Drayna, out of eight potential "clues" on this test for intoxication, Renz exhibited two.

The finger-to-nose test requires the taker to close his eyes, tip his head back, and first place the right index finger on the tip of the nose, then the left index finger. Renz did touch the tip of his nose with his right index finger but with his left index finger he touched the upper bridge of his nose. He did not sway and had good balance while performing this test.

Officer Drayna testified that he administered a fifth test, the horizontal gaze nystagmus (HGN), which tests for jerkiness of the eyes. However, the trial court sustained Renz's objection to Officer Drayna's testimony on the administration and results of this test. The court ruled that expert testimony was needed to establish that the HGN was a test that a lay person could administer and interpret and to establish that the test was a valid indicator of intoxication.

After administering the field sobriety tests, Officer Drayna asked Renz to provide a breath sample for the PBT, and Renz did so. The result of that test was .18. The officer then placed Renz under arrest. Renz was cooperative throughout his contact with Officer Drayna.

The trial court ruled that the initial stop was lawful because the officer, upon hearing the exhaust even though the windows were rolled up and the radio was on, had probable cause to stop Renz for an equipment violation and at least reasonable suspicion to investigate.

With respect to the PBT, the court construed the statutory language to require a lower level of probable cause to request a PBT than that needed to make an arrest. The court carefully evaluated and commented on the evidence. It noted that there was "considerable evidence" that Renz was not under the influence of an intoxicant and it reviewed that evidence. In the court's view, the evidence that he "might be" under the influence of an intoxicant was the odor of intoxicants, Renz's admission that he drank three beers earlier, losing his balance on the heel-to-toe test and not keeping his heel and toe touching when walking as instructed, and missing the tip of his nose with his left hand on the finger-to-nose test. Based on that evidence, the court concluded the officer "marginally had probable cause to request a [PBT]." At the time the court made this ruling, Drayna had not yet testified that by "losing balance" on the heel-to-toe test he meant stepping off the imaginary line; that while performing the finger-to-nose test Renz maintained his balance; and that Renz swayed during the heel-to-toe test. After hearing this additional testimony, the court reaffirmed its ruling that this was a case of "marginal probable cause," with the first two pieces of additional testimony favoring Renz and the third favoring the County. The court also ruled that, with the PBT results, there was probable cause to arrest for OWI.

DISCUSSION

Vagueness Challenge § 347.39, Stats.

We first address Renz's contention that the muffler statute violates the due process clause because it is vague. This presents a question of law, which we review de novo. See State v. Pittman, 174 Wis.2d 255, 276, 496 N.W.2d 74, 83 (1993). The presumption is that the statute is constitutional and the challenger has the burden of showing beyond a reasonable doubt that it is not. State v. White, 180 Wis.2d 203, 213, 509 N.W.2d 434, 437 (Ct.App. 1993). A statute or ordinance is unconstitutionally vague if, because of some ambiguity or uncertainty in the gross outlines of the conduct prohibited, persons of ordinary intelligence do not have fair notice of the prohibition, and those who enforce the laws lack objective standards and may operate arbitrarily. Pittman, 174 Wis.2d at 276, 496 N.W.2d at 83. The first part of the test is concerned with whether the statute or ordinance sufficiently warns persons who wish to obey the law that their conduct comes near the proscribed area. Id. The second part is concerned with whether those who enforce and apply the law may do so without creating or applying their own standards. Id.

If, by the ordinary process of statutory construction, we can give practical or sensible meaning to the statute, it is not void for vagueness. State v. Smith, 215 Wis.2d 84, 91-92, 572 N.W.2d 496, 498-99 (Ct.App. 1997). The ordinary process of statutory construction begins with the language of the statute, which we interpret according to its common meaning. See State v. Sample, 215 Wis.2d 486, 494, 573 N.W.2d 187, 190 (1998).

Renz argues that the statute provides no objective standard for law enforcement personnel and therefore permits them to create their own subjective standards and to operate arbitrarily. In particular, he contends that the terms "excessive" and "unusual" to describe "noise" simply call for subjective opinions of individuals, and he contrasts this language with that of an anti-noise ordinance found not unconstitutionally vague in City of Madison v. Bauman, 162 Wis.2d 660, 676-79, 470 N.W.2d 296 (1991). That ordinance prohibited a person from "making any noise tending to unreasonably disturb the peace and quiet of persons in the vicinity thereof. . . ." Id. at 665, 470 N.W.2d at 297. The court rejected the argument that "unreasonably" depended upon a subjective reaction of one in the vicinity, holding that it provided a sufficient standard to prevent excessive discretion and guide people in their conduct. Id. at 681, 470 N.W.2d at 304. While acknowledging that what is reasonable always depends on the circumstances, the court decided that the circumstances were sufficiently spelled out in the ordinance: what a reasonable person would conclude would disturb the peace and quiet of the vicinity. Id. at 678, 470 N.W.2d at 302.

Bauman undercuts, rather than supports, Renz's position. The ordinary rules of statutory construction permit us to use a dictionary to ascertain the common meaning of statutory language, and consulting a dictionary for that purpose does not render a statute ambiguous. See Sample, 215 Wis.2d at 498-99, 573 N.W.2d at 192. The dictionary definition of "excessive" is "exceeding a normal, usual, reasonable, or proper limit." American Heritage College Dictionary 477 (3d ed. 1995). Thus excessive noise means "unreasonable noise"; and the concept of reasonableness is sufficiently definite to satisfy the vagueness test if the circumstances are sufficiently spelled out. See Bauman, 162 Wis.2d at 681, 470 N.W.2d at 304.

Renz argues that the statute does not sufficiently spell out the circumstances within which the judgment of excessive or unusual noise is to be made. We disagree. The first subsection requires that a vehicle be equipped with "an adequate muffler in constant operation and properly maintained to prevent any excessive or unusual noise. . . ." Section 347.39(1), Stats. The second subsection prohibits specific modifications to a muffler or exhaust system, as well as any modification that "will amplify or increase the noise emitted by the motor of such vehicle above that emitted by the muffler originally installed on the vehicle, and such original muffler shall comply with all the requirements of this section." Section 347.39(2). The third section defines "muffler." These sections make clear that excessive or unusual noise is to be judged against the noise emitted by a muffler that meets the statutory requirements when originally installed on the vehicle. This is a sufficiently specific context in which to judge the reasonableness of the noise emitted by a muffler.

Looking to the manner in which Officer Drayna interpreted the ordinance, we are persuaded, as was the court in Bauman, that the officer understood and properly applied the statutory standard. See Bauman, 162 Wis.2d at 680-81, 470 N.W.2d at 304. Officer Drayna understood that the standard for a reasonable, usual or normal amount of noise was that amount of noise emitted when a muffler was originally installed on a car. He knew what that sounded like and he knew this sound was louder, so loud that he could hear it with his windows up and his radio on. His judgment that the muffler was defective and the noise was greater than that of a car with a properly maintained muffler was confirmed by Renz, who acknowledged that the muffler "had leaks and was loud." We conclude § 347.39, Stats., does provide an objective standard for law enforcement officers to employ and Officer Drayna applied that standard, not an arbitrary or subjective one, when he stopped Renz. The statute is not unconstitutionally vague.

Interpretation of "Probable Cause" for PBT

Renz argues that the trial court erred in interpreting the "probable cause" required for a PBT under § 343.303, Stats., to be a lesser standard than probable cause to arrest for a violation of the OWI statute, § 346.63(1)(a), Stats. This presents an issue of statutory construction, a question of law, and our review is de novo. See State v. Setagord, 211 Wis.2d 397, 405-06, 565 N.W.2d 506, 509 (1997). The purpose of statutory interpretation is to discern the intent of the legislature. Id. To do so, we first consider the language of the statute. If the language of the statute clearly and unambiguously sets forth the legislative intent, we apply that to the case at hand and do not look beyond the statutory language to ascertain its meaning. Id. A statute is ambiguous when it is capable of being understood in two or more different senses by reasonably well-informed persons. Id. at 406, 565 N.W.2d at 510. If a statute is ambiguous, we look to the scope, history, context, subject matter and object of the statute in order to ascertain legislative intent. Id.

Section 343.303, Stats., provides in part:

If a law enforcement officer has probable cause to believe that the person is violating or has violated s. 346.63(1) . . . the officer, prior to an arrest, may request the person to provide a sample of his or her breath for a [PBT] using a device approved by the department for this purpose. The result of the [PBT] may be used by the . . . officer for the purpose of deciding whether or not the person shall be arrested for a violation of s. 346.63(1) . . . and whether or not to require or request chemical tests as authorized under s. 343.305(3).

Renz's interpretation of the statute is a reasonable one. Probable cause in the context of arrest is well defined in the case law. It refers to that quantum of evidence that would lead a reasonable police officer to believe that a person probably committed a crime, State v. Paszek, 50 Wis.2d 619, 624, 184 N.W. 839 (1971), or, in this context, committed a violation of § 346.63(1), Stats. See State v. Babbitt, 188 Wis.2d 349, 356, 525 N.W.2d 102, 104 (Ct.App. 1994). The evidence giving rise to such probable cause need not be sufficient to prove guilt beyond a reasonable doubt, nor sufficient to prove that guilt is more probable than not; it is only necessary that the information lead a reasonable officer to believe that guilt is more than a possibility. Paszek, 50 Wis.2d at 625, 184 N.W.2d at 839. It is reasonable to assume that the legislature was well aware of this case law definition when it chose the words "probable cause to believe that a person is violating or has violated s. 346.63(1)."

The County responds that the probable cause required to request a PBT must be a lesser standard than the probable cause required for an arrest after a PBT is administered because otherwise the PBT is not necessary. We understand this to be the trial court's rationale as well. We grant this is also a reasonable interpretation of the statute; however, after considering the purpose, context and history of the statute, we conclude that the more reasonable interpretation is that the probable cause required for a PBT is the same standard as probable cause to arrest for a violation of § 346.63(1)(a), Stats.

We observe first that in § 343.303, Stats., the legislature has chosen a different term to describe the standard for administering a PBT test with respect to operators of commercial vehicles — detecting "any presence" of an intoxicant or having "reason to believe" the person violated § 346.63(7), Stats. Section 346.63(7) is stricter than § 346.63(1) in that it prohibits a person operating a motor vehicle from having an alcohol concentration above 0.0, operating or being on duty within four hours of drinking any intoxicating beverage and possessing an intoxicating beverage. The legislature's choice of "reason to believe" as the standard necessary to trigger a request for a PBT test with regard to the stricter statute indicates that the legislature could have used a term other than "probable cause" to trigger a request for a PBT with respect to the § 346.63(1), but chose not to.

Indeed, the legislative history of § 343.303, Stats., shows that, during the process that led to its enactment, the senate considered and rejected substituting "reason to believe . . . a person is violating or has violated s. 346.63(1) . . ." for the proposed language "probable cause to believe. . ." in the first sentence. There was also a draft proposing "[i]f a law enforcement officer reasonably suspects the person is violating or has violated s. 346.63(1). . . ." as the standard While we are unaware of case law establishing the meaning of "reason to believe" in a similar or analogous context, the term "reasonable suspicion" has a well-developed meaning in Fourth Amendment case law. Temporary detentions for the purpose of investigation are seizures within the meaning of the Fourth Amendment and are constitutionally permissible if the officer has a reasonable suspicion that some kind of criminal activity has been or will be committed, Terry v. Ohio, 392 U.S. 1, 22 (1968), or if a traffic violation has been or will be committed. See State v. Gaulrapp, 207 Wis.2d 600, 605, 558 N.W.2d 696, 698 (Ct.App. 1996). See also § 968.24, Stats., codifying the Terry standard. Reasonable suspicion in this context is a lesser standard than probable cause to arrest and exists when specific and articuable facts available to the officer, together with the rationale inferences from those facts, would warrant an officer of reasonable caution to suspect criminal activity. See State v. Goebel, 103 Wis.2d 203, 208-09, 307 N.W.2d 915, 918 (1981) (citing Terry, 392 U.S. at 21-22).

The fact that the legislature did not adopt the "reason to believe" or "reasonable suspicion" language, but instead adopted "probable cause to believe," is a persuasive indicator that it intended to adopt the probable cause standard as defined in the case law, rather than a lesser standard.

We acknowledge that requiring probable cause to arrest before requesting a PBT limits the conditions under which a PBT may be requested and undercuts the use of a PBT to establish probable cause to arrest. However, it does not deprive § 343.303, Stats., of all meaning or function. Even if an officer has probable cause to arrest, he or she may decide to request a PBT first, and then use the results in deciding whether to actually make an arrest.

On balance, we are persuaded that the legislature intended that an officer must have probable cause to arrest a person for a violation of § 346.63(1)(a), Stats., before the officer may request a PBT. The term "probable cause" in this context is so well defined in the case law that we would not expect the legislature to employ this term to mean something else without any indication in the statute of what that other standard might be. The legislative history supports this conclusion in that it demonstrates that other terms were considered and rejected — at least one of them carrying a well-defined meaning as a lesser standard than "probable cause."

Probable Cause Analysis in this Case

We now turn to the question whether Officer Drayna had probable cause to arrest Renz for violating § 346.63(1)(a), Stats., before requesting that he submit to a PBT. We consider all the facts and circumstances within the officer's knowledge at that time. Paszek, 50 Wis.2d at 625, 184 N.W.2d at 840. We do not disturb the findings of the trial court unless they are clearly erroneous. See State v. Richardson, 156 Wis.2d 128, 137-38, 456 N.W.2d 830, 833 (1990). However, whether those facts meet the statutory standard is a question of law, which we review de novo. See id. Although our review is de novo, and although we are applying a different standard than did the trial court with respect to the PBT, we benefit from the trial court's careful analysis of the evidence. We note that the court concluded that the evidence only "marginally" met a lesser standard of probable cause than we employ in our independent review.

We begin by observing that § 346.63(1)(a), Stats., does not prohibit operating a motor vehicle after having consumed alcohol, but prohibits driving "[u]nder the influence of an intoxicant . . . to a degree which renders [one] incapable of safely driving." Therefore, although it is undisputed that Renz said he had three beers earlier in the evening and the officer detected a strong odor of alcohol, more is needed to establish probable cause to believe Renz violated the statute. We identify the following evidence that might indicate that the alcohol affected Renz's capacity to drive safely: Renz did not stand on one leg for thirty continuous seconds but put his foot down on eighteen, then started over at ten and continued to thirty; he stepped off the imaginary line at step seven on the walk-and-turn test; he appeared unsteady on the walk-and-turn test; he left one-half to one inch between his heel and toe on the walk-and-turn test; and he touched his left hand to the bridge of his nose rather than to the tip of his nose on the finger-to-nose test.

With respect to the finger-to-nose test, the trial court in its initial comments on probable cause stated its assumption that this tested for balance. During later cross-examination, Officer Drayna testified that this was not a test for balance but he did not explain what it did test for or the significance of touching the bridge of the nose rather than the tip of the nose. The trial court apparently accepted the officer's testimony that the finger-to-nose test did not test for balance, and that Renz maintained his balance during this test, but made no findings on the purpose of this test. We assume it tests for coordination, but, without any testimony indicating the relevance of touching the bridge of one's nose rather than the tip, or any trial court findings, we cannot attach much significance to that discrepancy as an indicator of incapacity to drive safely.

Officer Drayna did not explain the significance of leaving a space of one-half to one inch between heel and toe, and the court made no findings on that. We assume this goes to either balance or ability to follow directions. However, in the absence of some explanatory testimony this evidence, too, has minimal significance for the capacity to drive safely.

It is common knowledge that unsteadiness is one symptom of intoxication and may impair the capacity to drive safely. Based on common knowledge and experience, swaying while walking heel to toe on the imaginary line is evidence of unsteadiness, and stepping off the imaginary line may be as well. The trial court did not consider putting one leg down after eighteen seconds rather than thirty seconds to be an indication of unsteadiness, but we conclude it may be.

We must now view the evidence indicating unsteadiness in the context of all the circumstances known to Officer Drayna. Renz's driving did not indicate that he could not drive safely. His speech was not slurred, there was no testimony that his eyes were glassy, and he was not unsteady when walking or standing apart from the field sobriety tests. He performed the alphabet test correctly. On the walk-and-turn test and the one-legged stand test, there were a number of other "clues" that Officer Drayna looked for as signs indicating intoxication, and those were not present — three on the one-legged stand and six on the walk-and-turn. With respect to the significance of the three "clues" of intoxication that Officer Drayna did observe — one on the one-legged stand and two on the walk-and-turn — Officer Drayna explained that these two tests and the HGN "are all three put together. It's a battery of tests. The clues mean nothing if you don't count them all."

We conclude that the instances of Renz's unsteadiness, when considered in the context of all the evidence that he was not under the influence of an intoxicant, are minimal and do not demonstrate that there was "more than a possibility" that he was under the influence of an intoxicant to the degree that made him incapable of driving safely. We therefore conclude Officer Drayna did not have probable cause to arrest at the time he asked Renz to submit to a PBT.

We agree with Renz that since there was not probable cause to believe that Renz had violated or was violating § 343.63(1)(a), Stats., when Officer Drayna requested the PBT, the results of that test were not admissible at the hearing on Renz's motion to suppress. The statute establishes the conditions for requesting a PBT. See State v. Beaver, 181 Wis.2d 959, 969, 512 N.W.2d 254 (Ct.App. 1994) ("The thrust of [ 343.303] is to give a police officer the authority to request a driver to submit to a PBT."). The statute also establishes the circumstances in which it is admissible. We conclude that the only reasonable construction of the statute is that the PBT is not admissible to show probable cause for arrest when an officer requested a PBT without having probable cause to believe there had been a violation of § 343.63(1)(a), or the other applicable statutes enumerated in § 343.303, Stats. As we have already concluded in this case, there was not probable cause to arrest without the PBT results. We therefore reverse the judgment of conviction and the trial court's order denying Renz's motion to suppress evidence.

By the Court. — Judgment reversed.