Abstract: Provided is a monomer composition containing methyl methacrylate and methyl isobutyrate, in which the methyl isobutyrate content is more than 300 ppm by mass and 50,000 ppm by mass or less relative to the total mass of the monomer composition.

Abstract: Provided is a monomer composition containing methyl methacrylate and methyl propionate, in which the methyl propionate content is more than 200 ppm by mass and 50,000 ppm by mass or less relative to the total mass of the monomer composition.

Abstract: Provided is a monomer composition containing methyl methacrylate, and at least one compound of methyl pyruvate and methyl 2-methylbutyrate.

Abstract: A numerically controlled machine tool for machining a non-circular workpiece according to profile data. The numerical controller stores phase compensation values and position compensation data files in connection with the types of cam and the various rotational speeds of the main spindle. Each position compensation data file consists of a series of position compensation values for a successive rotational positions of the main spindle. The numerical controller searches a phase compensation value and a position compensation data file according to the type of cam to be ground and the rotational speed of the main spindle during the grinding operation. Thereafter, the numerical controller offsets the read-out position of the profile data by the amount corresponding to the searched phase compensation value, and compensates each profile data with position compensation data stored in the searched file so as to eliminate a machining error which changes depending upon the rotational speed of the main spindle.