Although this action was referred to a master (the plaintiff claims erroneously) as a "Non-Jury Action" and despite the plaintiff's failure to object to that reference prior to the filing of her objections to the master's report (which was confirmed by the judge), she properly relied upon the demand for a jury trial made by the defendant Chrysler Credit Corporation pursuant to the provisions of Mass.R.Civ.P. 38(b), 365 Mass. 801 (1974). Nothing occurred to transform the case into a nonjury trial pursuant to the provisions of Mass.R.Civ.P. 39(a), 365 Mass. 801 (1974), which provides that "[w]hen trial by jury has been demanded as provided in Rule 38, the action shall be designated upon the docket as a jury action. The trial of all issues so demanded shall be by jury, unless (1) the parties or their attorneys of record, by written stipulation filed with the court or by an oral stipulation made in open court and entered in the record, consent to trial by the court sitting without a jury." See Vaught Constr. Corp. v. Bertonazzi Buick Co., 371 Mass. 553 , 557-558 (1976). With respect to the defendants' unsuccessful assertion that the plaintiff's conduct constituted a waiver of her right to a jury trial, see Star Sales & Distrib. Corp. v. A.B.C. Drywall Co., 6 Mass. App. Ct. 866 (1978), and cases cited. The judgment is vacated and the case remanded to the Superior Court for a trial by jury at which the master's report is to be treated as though the original order of reference to the master had been designated as a "Jury" rather than a "Non-Jury" action. See Mass.R.Civ.P. 53(e)(3), 365 Mass. 820 (1974).

So ordered.

1. Following the decision of the Supreme Judicial Court in Vyskocil v. Vyskocil, 376 Mass. 137 (1978), a single justice of this court

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allowed the plaintiff's motion for an extension of time to comply with the requirements of Mass.R.A.P. 9(c), 365 Mass. 852 (1974), and the order of the Probate Court dismissing the appeal must accordingly be reversed. 376 Mass. at 141. 2. The judge erred in concluding that the defendant's obligation under the "additional alimony" provisions of the Minnesota divorce judgment (which was based upon and incorporated the parties' written agreement) was to pay as additional alimony one-third of net, rather than gross, increases in salary over the base figure. If the parties' intention is left ambiguous by the use of the words "a sum equal to one third . . . of any salary increases, bonus or compensation, over and above the basic figure of . . . $25,000 per year," the ambiguity is resolved by the undisputed facts that (1) the defendant's gross salary in the year the parties signed the agreement was $24,879.82, (2) the provision for base alimony, $660 per month, amounted to approximately one third of the gross, rather than the net, salary, and (3) the parties' conduct since the agreement went into effect indicates that they interpreted the additional alimony provision as being triggered by increases which put the defendant's gross, but not his net, salary above $25,000. The hybrid interpretation suggested by the defendant, that an increase in gross salary triggers the payment of additional alimony, but the additional alimony payable is limited to one-third of the increase in net salary, is plainly at variance with the words employed. 3. The judge properly denied the plaintiff's claim for reimbursement of certain sums spent for special tutoring and remedial instruction, not because of his finding (which was warranted by the evidence) that the daughter did not have dyslexia, but because of his finding that the instruction was educational, rather than medical, in nature and was thus governed by the educational expense provisions, rather than the medical expense provisions, of the parties' unusually detailed agreement. The finding in question was plainly warranted and we decline to disturb it. 4. The order dismissing the appeal is reversed. The judgment is reversed. The case is remanded to the Probate Court for further proceedings consistent with part 2 hereof.

So ordered.