What do the mathematical units m, cm, DM2, cm2, M2, DM mean

What do the mathematical units m, cm, DM2, cm2, M2, DM mean

Meter, centimeter, square decimeter, square centimeter, square meter, decimeter

What is the mathematical unit symbol DM2

Square decimeter

Interesting things about Mathematics

One afternoon's self-study class, the teacher arranged us to do homework (about Mathematics), said: who finished the day's math homework can go home first! The teacher himself in the podium to change homework! Brother was a good student in those days, 40 minutes of self-study class, only 15 minutes later, I almost finished writing, because I was too involved in writing, I forgot it was in class