Q:

What does the "2" indicate in 2:4 format for Excellon drill files?

For Excellon drill files, I know that the number after the colon indicates the precision, i.e.

2:3 has 1 mil resolution
2:4 has 0.1 mil resolution 
2:5 has 0.01 mil resolution

However, I don't know what the number before the colon indicates.  What does the "2" mean?

A:

The number before the colon designates the whole number digits, while the number after the colon indicates the number of precision digits.
For example, the number "37.294" would be represented in the following way:

3:4 - 037.2940
2:4 - 37.2940
2:3 - 37.294

