GTTF Mouse Colony
There are different ear notch systems. The GTTF uses the one described in Manipulating the Mouse Embryo - A Laboratory Manual (ref.). This system allows mice to be numbered from 1 to 99.
5 = 1 + 4
6 = 2 + 4
7 = 3 + 4
8 = 1 + 2
9 = 2 + 3
50 = 10 + 40
60 = 20 + 40
70 = 30 + 40
80 = 10 + 20
90 = 20 + 30
Reference:
Hogan B, Beddington R, Costantini F and Lacy E, ed. 1994. Manipulating the Mouse Embryo - A Laboratory Manual, 2nd ed. Cold Spring Harbor Laboratory Press.