"The trial court was thoroughly acquainted with all the facts and circumstances involved as the parties have been before the court many times in the past 7 or 8 years. It is primarily a question for the trial court to determine whether the defendant made an adequate showing of a changed financial condition, and that tribunal has consistently refused to modify the decree for either party." In Adams v. Adams, 281 Mich. 448, we said: "Plaintiff complains because the decree, although awarding her custody of the minor son, permits defendant to have the custody on Saturday and Sunday afternoons and for a month in the summer.