Just to be clear, at least in my mind.

The only weird number is -1 for zero. zero essentially does not exist all on it's own in ProConnect.

There are dropdown choices that are numbered. If you remember the number it makes input quicker. e.g. Linking a depreciation item to an activity involves using the drop down, or if you remember 3 is rental, then just enter the 3. 

Some others are yes or no answers using 1 or  2. 

It is different than some other programs, but they all have their "different" way of doing things.

Good luck.