HULL, J.

The sole issue on this appeal is whether a municipal assessor has the power, under General Statutes 12-55, to increase a real property assessment between decennial revaluations on the ground that a sale of the property in question demonstrates that the property has greatly increased in value in relation to other properties in the municipality. We conclude that although an assessor, absent unusual circumstances that do not exist in this case, cannot be required to make such an interim revaluation of real property, he may do so in accordance with 12-55, under appropriate circumstances.

This action involves a tax appeal by the plaintiff from a decision of the defendant which affirmed the town assessor's upward reassessment of the plaintiff's property for the 1984, 1985 and 1986 tax years. The plaintiff claimed that the reassessment was excessive and illegal and that, as a result, the plaintiff's property bore a disproportionate share of the tax burden in the town of Rocky Hill. The plaintiff moved for summary judgment, claiming, inter alia, that as a matter of law the defendant was barred from reassessing the plaintiff's property under the provisions of General Statutes 1262. The court denied that motion. The court, in its memorandum of decision, stated that the plaintiff's reliance on Uniroyal, Inc. v. Board of Tax Review, 182 Conn. 619, 438 A.2d 782 (1981), for its claim that 12-62 precludes interim revaluations, was misplaced. The court noted that, despite dicta in Uniroyal, Inc., that pursuant to 12-62 "revaluation . . . need only be available once each decade," the Uniroyal, Inc. court did not hold that more frequent revaluations are illegal.

The court noted that a judgment of the Superior Court in 1982 found the fair market value of the property in question for the years 1979, 1980 and 1981 to be $23,820,950. It further noted that in 1984 the plaintiff purchased the property for $57,539,739, an increase in value of 141 percent. The court relied on the affidavit of the Rocky Hill tax assessor that stated that he had examined that sale "in light of all other recent residential and commercial property sales in Rocky Hill and found the assessment on the subject property to be grossly out of line with other assessments in the municipality . . . Therefore, on October 1, 1984, he reassessed the plaintiff's property pursuant to General Statutes 12-55 and 12-62 in order to keep the plaintiff's assessment consistent with other property assessments in the municipality." The court then concluded that the language of 12-55 providing that "[t]he assessors may increase or decrease the valuation of property as named in any of such lists or in the last-preceding grand list," when read with the language in 12-64 providing that all property "shall be liable to taxation at a uniform percentage of its present true and actual valuation . . . to be determined by the assessors," empowered assessors to make interim adjustments in assessments. Finally the court stated that "a question of fact exists as to the method the assessor used in making his revaluation and whether or not it conformed to Sec. 12-64."

The plaintiff then moved for reargument of its motion for summary judgment, claiming that the case of Ralston Purina Co. v. Board of Tax Review, 203 Conn. 425, 439-41, 525 A.2d 91 (1987), held that assessors are "precluded" from making interim revaluations based on a change in the fair market value of the property "attributable solely to changes in the market conditions." The court concluded that Ralston Purina Co. "clearly holds that the decennial revaluations of real property mandated by General Statutes 12-62 [are] the exclusive remedy for the town to deal with changes in market values, and more frequent adjustments are not permitted." The court then rescinded its earlier decision denying the plaintiff's motion for summary judgment and granted it. The defendant appealed from the judgment granting the plaintiff's motion for summary judgment, claiming that the assessor had the power under 12-55 to adjust the assessment in the interim years between decennial revaluations on the ground that the sale of the property in question shows that the property has greatly increased in value in relation to other properties in town.

The facts as found in the court's memorandum of decision, dated June 30, 1987, on the plaintiff's motion for reargument are not in dispute. The plaintiff is the owner of a 941 unit apartment complex known as Century Hills located in Rocky Hill. Pursuant to General Statutes 12-62, the town of Rocky Hill conducted a general revaluation of local real estate, effective October 1, 1979. The plaintiff's predecessor in title had contested the 1979 revaluation for the years 1979, 1980 and 1981, which resulted in a final judgment that the true and actual valuation of the property for those years was $23,820,950 and that the assessment should be 70 percent of that figure. The plaintiff purchased the property on March 29, 1984, for $57,339,737. After that purchase, the tax assessor revalued and reassessed the plaintiff's property, finding the true valuation of the property as of October 1, 1984, to be $41,987,500 and the assessed value $29,391,250

The assessor stated in his affidavit that he "reassessed the subject property in light of the sale to the plaintiff and in light of the most recent assessment ratio available on or about October 1, 1984. The revaluation and reassessment was not based on any new construction, physical improvements or changes in the use of the subject property."

In Ralston Purina Co., the plaintiffs appealed to the Superior Court, pursuant to General Statutes 12-118, from the refusal of the defendant board of tax review of the town of Franklin to reduce the October 1, 1982 tax assessments on their real and personal property in that town. The plaintiffs had claimed that the fair market value of their property had declined substantially since the last decennial revaluation conducted by the town, as evidenced by the subsequent sale of the property in 1983 at a price significantly below its assessed value. Ralston Purina Co. v. Board of Tax Review, supra, 428. The trial court did not discuss whether either of the plaintiffs was entitled to an interim adjustment of its property assessment, but adopted the implicit conclusion of an earlier judge in the case that the defendant was obligated to make such adjustments. The trial court sustained the appeals and ordered a reduction in the assessed values of the properties. This court found error in the court's ruling that the board of tax review was required, as a matter of law, to adjust the plaintiffs' tax assessments in the interim between decennial revaluations of the real property. We noted that an appeal under General Statutes 12-118 conditions relief upon proof of failure to comply with 12-64, which in turn provides that all real estate "`shall be liable to taxation at a uniform percentage of its present true and actual valuation . . . to be determined by the assessors.'" Id., 434. The defendant in Ralston Purina Co. v. Board of Tax Review, supra, 435, relied principally on the language of General Statutes 12-62 and this court's interpretation of that statute in Uniroyal, Inc. v. Board of Tax Review, supra. The defendant board conceded that, under certain circumstances, such as the destruction or expansion of property, a substantial change in its use or zoning classification, or a decision by the taxpayer to go out of business, it would be required to conduct an interim revaluation of property. Ralston Purina Co. v. Board of Tax Review, supra, 436.

The plaintiffs in Ralston Purina Co. argued that although 12-62 requires revaluation of real estate at least every ten years it does not preclude such revaluation in appropriate circumstances. They emphasized particularly the express language of 12-64 which provides that all nonexempt real property shall be taxed at its "present true and actual valuation," defined in General Statutes 12-63 as the "fair market value thereof and not its value at a forced or auction sale." The plaintiffs then claimed that an adjustment in their assessments was required pursuant to General Statutes 12-55 which states in part that "assessors may increase or decrease the valuation of property as named in . . . the last-preceding grand list." The plaintiffs conceded that 12-55 appeared to be permissive but that when read in context with 12-62 through 12-64 it mandates the reassessment they sought. Ralston Purina Co. v. Board of Tax Review, supra, 436-37.

This court noted that the issue of whether assessors are required to conduct interim revaluations of property to account for the effect of changes in market conditions was not addressed by the pertinent statutes. The court then stated: "The plaintiffs' reading of the statutes, standing alone, is therefore as plausible as the defendant's interpretation. . . . [H]owever, the plaintiffs' argument directly contradicts our interpretation of 12-62 in [Uniroyal, Inc. v. Board of Tax Review, supra]." (Emphasis added.) Id., 437.

We then stated: "We held in [Uniroyal, Inc.,] that the decennial revaluation of real property mandated by 12-62 is the exclusive remedy provided by the legislature `for variations in the effect of market conditions on different parcels . . .' [Uniroyal, Inc. v. Board of Tax Review, supra, 629]. Indeed, the procedure established in 12-62 reflects the legislative judgment that the remedy of revaluation `need only be available once each decade,' rather than any time property values fluctuate in response to market conditions. [Id.]; see Kays, Inc. v. Board of Tax Review, [ 170 Conn. 477, 480, 365 A.2d 1207 (1976)]; Bassett v. Rose, 141 Conn. 129, 134-35, 104 A.2d 212 (1954). The plaintiffs' reliance upon 12-64 is therefore misplaced because 12-64, in contrast to 12-62, `is concerned with the manner of taxation, not the frequency of valuation, and it does not purport to require assessors to be updated on their valuations at all times.' Kays, Inc. v. Board of Tax Review, supra; [Uniroyal, Inc. v. Board of Tax Review, supra, 629]." Id., 437-38.

This court concluded that the legislature was aware that "even though property values may fluctuate within a ten year period, it is neither realistic nor necessarily desirable to require more frequent property revaluations." Id., 438. The court found that it was bound by the interpretation of 12-62 in Uniroyal, Inc., since the plaintiffs did not provide a convincing rationale for the court to depart from that interpretation. Id., 439. "Since the legislature has not amended 12-62 subsequent to our decision in Uniroyal, Inc., we can discern no reason now to amend that statute judicially so as to alter the apparent intent of its drafters to preclude, as a general rule, interim revaluations of real property." Id.

The plaintiffs in Ralston Purina Co. attempted to distinguish Uniroyal, Inc., on the ground that the plaintiffs in that case claimed that they were bearing a disproportionately high burden of taxes while in Ralston Purina Co. they claimed only that the fair market value of their property had declined in the interim period between decennial revaluations. In Ralston Purina Co., we declared: "In the context of this case, however, this distinction has no significance. Although the plaintiffs here rely upon different grounds in challenging their tax assessments, they seek the same relief requested by the plaintiffs and denied by this court in [Uniroyal, Inc.,] an interim revaluation of their property. As we concluded in [Uniroyal, Inc. v. Board of Tax Review, supra, 629], the legislature, in 12-62, has precluded such interim revaluations except in unusual circumstances, which did not exist in that case and likewise do not exist here. The plaintiffs presently before us are therefore no more entitled to an interim adjustment of their tax assessments than were the plaintiffs in [Uniroyal, Inc.]" Id., 440. The court remanded both cases with direction to render judgments for the defendant.

The defendant in this case first argues that the Ralston Purina Co. ruling denying mandatory interim revaluation does not apply to a case where the board is operating permissively under 12-55. The defendant argues that, except for the generally recognized narrow exceptions where interim reassessment is allowed, the board and the assessors would have a greatly restricted function if they were not able to equalize assessments between decennial revaluations. It claims that just as 12-55 states that an assessor "shall equalize" the lists "if necessary," General Statutes 12-111 states that "[s]uch board [of tax review] may equalize and adjust the valuations and assessment lists of such town[s] . . ."

In its second briefed argument, the defendant, citing Kays, Inc. v. Board of Tax Review, supra, claims that its interpretation of the effect of 12-55 does not leave the taxpayer unprotected because he has a remedy if he shows that he has assumed a disproportionate tax burden, a claim the plaintiffs in Ralston Purina Co. did not make. The defendant claims that the Ralston Purina Co. majority's statement that the lack of an allegation in that case of a disproportionate burden "has no significance" contradicts Uniroyal, Inc.'s pronouncement that "`[t]he plaintiffs would be entitled to relief under 12-118 if [they] could prove that [their] property was bearing a disproportionately high tax burden because of the defendant's failure to comply with 12-64.'" Uniroyal, Inc. v. Board of Tax Review, supra, 626. Thus, it finally argues, the assessor's remedy under 12-55 when a taxpayer's assessment is disproportionately low is the corollary of the taxpayer's remedy under 12-118 when his assessment is disproportionately high.

The plaintiff in its brief relies solidly on language previously cited in Ralston Purina Co., which in turn cited Uniroyal, Inc., to the effect that an increase or decrease in the sale price of real property which reflects a change in market conditions may only be adjusted as part of a general revaluation pursuant to 12-62. The plaintiff quotes the Uniroyal, Inc. court which stated that the average ratio of the assessed values of properties to their actual selling prices was "not applicable to discrepancies in valuation which arise during the ten-year period between valuations." Uniroyal, Inc. v. Board of Tax Review, supra, 630.

The plaintiff stresses that the limitation on the assessor's power to make interim revaluations, only in the unusual circumstances referred to in Ralston Purina Co. v. Board of Tax Review, supra, 435-46, is also reflected in two statutory exceptions, General Statutes 12-53a, permitting a reassessment where new construction is completed on property between revaluations, and General Statutes 12-64a, authorizing a reduction in the assessed value of property upon the demolition and removal of damaged buildings.

The plaintiff points out that the defendant's argument is exactly that raised by Justice Shea's dissent in Ralston Purina Co., when Justice Shea argued that 12-55 should be read to authorize assessors to "increase or decrease the valuation of property" in fulfillment of their duty to "equalize" the annual tax lists of a town but only "when special circumstances pertaining only to one property result in a substantial change in its value." Id., 442. The plaintiffs concluding argument is that 12-55 is no more than an administrative statute which sets forth the procedure for noticing a change in the valuation of property. It provides, the plaintiff claims, no independent authority upon which an assessor may rely in making such a change, other than permitting the making of assessments "omitted by mistake" or "required by law."

We look first to the holding in Uniroyal, Inc. v. Board of Tax Review, supra. The plaintiffs, pursuant to 12-118, appealed to the Superior Court from the refusal of the board of tax review to reduce the valuation of its land and buildings in Middlebury. The trial court rendered judgment for the defendant on the ground that the plaintiffs were not aggrieved by the action of the board and the plaintiffs appealed to this court. Id., 620.

Although not explicitly articulated in Uniroyal, Inc., it is clear from the above facts that the plaintiffs were seeking mandatory interim revaluation. Their first argument was that the trial court erred in not concluding that their property was bearing a disproportionately high burden of taxes in Middlebury and in failing to equalize the tax burden to that of other property in the town. Id., 622. This court discussed 12-64, providing that all nonexempt real estate "shall be liable to taxation at a uniform percentage of its present, true and actual valuation to be determined by the assessors . . ." Id., 623. It then analyzed the plaintiffs' extensive expert testimony concerning the average ratio of the assessed values of Middlebury properties to their actual selling prices for certain years in question. Id. The court then discussed at length the use of average ratio analyses to establish the unfairness of assessment practices. Id. It then pointed out that the plaintiffs introduced the average ratio evidence in an effort to demonstrate that although the assessor applied a 65 percent valuation factor to their property, they actually applied a much lower valuation to other Middlebury property. It stated that "[s]uch a practice would violate the requirements of General Statutes 12-64. The plaintiffs would be `entitled to relief under 12-118 if [they] could prove that [their] property was bearing a disproportionately high tax burden because of the defendant's failure to comply with 12-64.' Hays, Inc. v. Board of Tax Review, 481, quoting Lerner Shops of Connecticut, Inc. v. Waterbury, [ 151 Conn. 79, 86, 193 A.2d 472 (1963).] As our cases indicate, relief under 12-118 is conditioned upon proof of failure to comply with 12-64." Id., 626.

The court then found that the average ratio evidence did not prove any violation of the statutory assessment scheme. Id., 627. The court concluded that the plaintiffs' property most likely benefited from continued use of the 1971 valuation figures for assessment purposes throughout the 1970s and the failure of the 1971 figures to reflect property value increases in subsequent years, as much as any other property owner. Such variation accruing within ten year periods is a permissible variation under 12-62. Id., 629. It then made the statement previously cited, that "in Connecticut, the remedy for variations in the effect of market conditions on different parcels is set forth in General Statutes 12-62. The remedy of revaluation was established by the legislature and it was the judgment of the legislature that the remedy need only be available once each decade." Id.

It is not necessary to consider the defendant's claim that there is a conflict between Ralston Purina Co. and Uniroyal, Inc., for in the context of this case this court's quotation in Ralston Purina Co. (p. 438) from Uniroyal, Inc., (p. 629) that the procedure in 12-62 "need only be available once each decade" is dicta. The language "need only be available" refers to a mandatory reassessment. That case has no bearing on the question of permissive interim revaluation as a power of the assessors under 12-55, nor did Uniroyal, Inc., on which Ralston Purina Co. relied, concern the question involved in this case. Further, the right of a taxpayer to seek interim relief under 12-118 on a claim of a disproportionate burden need not come into play. The resolution of the issue in this case requires only that we go directly to the plain language of 12-55, shorn of any irrelevant judicial gloss adhering to it.

Section 12-55 contains three operative phrases pertinent to our inquiry: (1) "When the lists of any town have been so received or made by the assessors, they shall equalize the same, if necessary"; (2) "make any assessment omitted by mistake or required by law"; and (3) "the assessors may increase or decrease the valuation of property as named in any such lists or in the last preceding grand list . . ." (There follow directions for notice to a taxpayer in the event of an increased assessment.) (Emphasis added.) There is no ambiguity in this broad grant of powers to assessors. It is a clear legislative mandate to grant to local assessors a continuing duty unrelated to decennial revaluations, to achieve administratively a fair and equal assessment for all taxpayers. The power to equalize the lists, if necessary, imports a watchtower role for the assessor to correct inequalities, whether too high or too low. The "if necessary" language clearly comprehends interim changes in assessments for there is no such requirement in 12-62 which mandates decennial revaluations. The latter have obviously been legislatively deemed necessary.

The plaintiff claims that 12-55 only authorizes changes "omitted by mistake" or "required by law." Such a restrictive interpretation ignores the plain language of the statute. The fact that these two additional powers are specifically set out does not in any way limit the broad power to equalize assessments provided for earlier in the statute. The most logical interpretation of the effect of these two additional powers is that in addition to the power to equalize assessments the assessors are also empowered to make these specified changes. Assessing property omitted by mistake is a common sense administrative duty having no relation to the "equalizing" function of the assessors. The same may be said of the added function of making any assessment "required by law." If it is required by law, the assessors are required to make it whether or not it is included in this section. Finally, the statute specifically gives to assessors the power to increase or decrease the value of assessed property. "`[S]tatutes should be construed so that no part of a legislative enactment is to be treated as insignificant and unnecessary, and there is a presumption of purpose behind every sentence, clause or phrase in a legislative enactment.'" State ex rel. Kennedy v. Frauwirth, 167 Conn. 165, 168, 355 A.2d 39 (1974). "In construing a statute, common sense must be used and we must assume that the legislature intended to accomplish a reasonable and rational result." Gentry v. Norwalk, 196 Conn. 596, 606, 494 A.2d 1206 (1985).

We conclude that the assessors in Rocky Hill did have the power under 12-55 to adjust a real estate assessment in the interim years between decennial revaluations on the ground that a sale of the property in question showed that the property had greatly increased in value in relation to other properties in the town. Because the summary judgment proceeding provided no occasion for the resolution of a disputed issue of fact, the necessary proof of such a disparate rise in value of the plaintiff's property has not been made in this case. The trial court declared in its memorandum of decision denying the plaintiff's first motion for summary judgment, that there existed a question of fact as to the method the assessor had used in making his revaluation and whether it conformed to 12-64. These and other issues of fact can only be resolved at trial.