A decimal is everything after the " . "(Actually it's the divider, but I think that's what you mean) sign in a number. Adventure capitalist only uses 3 decimals, even if the amount of money is very high. They change the suffix of the number instead, so that the player reads the number as very high, if you understand what I mean. When you start, if you have 142.240 dollars, there's only three numbers after the divider, and if you have 1.382 billion dollars, there's still only three numbers after the divider.

That works because when you reach a certain number, in AdCa case 999.999 dollars, the next dollar you make will change that number to 1 MILLION dollars, all the way up to 999.999 MILLION dollars, and then to 1 BILLION dollars. So the highest number you work with in that particular game is actually "only" 999999 (with a divider enter the third digit)

I hope this makes some sense, and you can search the forum for posts about using dividers, and using attributes for handling "large" numbers.

I hope this helps and that I haven't mislead you in any way