the if statements are checking specific characters in B1. if the last char is '.' then the O1 is assigned a value of 1 (no clue why it uses a formula instead of a value) then the dec01 routine is run. if the second last char in B1 is a '.' then O1 equals 2 and dec02 is run and so on
the first If statement is duplicated for some reason and the whole thing looks inefficient to me ;-)