I have no idea how to use it lol...

How do I know what the growth is?

AFAIK the best way is to look at the graphs at

http://bitcoin.sipa.be/ to get an idea.

I have one thought, tho the percentage is kind of confusing, Might I recommend just being able to type in 45 instead of 1.45?

The way it is done now indicates more clearly that you can enter values like 0.xx to simulate a negative growth. You might be right though, people could also enter the growth with a leading '-'. Since the calculator is now online for a few weeks it might not be such a good idea to change the input format afterwards, as it confuses the users.

Definitely a good choice. I think the remaining issue is that the difficulty probably can't be modeled as a geometric series. That is, although the last increase was ~16%, the one before that was like 80%, and the next one may be <10%. I'm not sure how you could take that into account.

Yes I am quite aware of this issue but I also see no way of simulating this. By analyzing the graphs at

http://bitcoin.sipa.be/ you could take the growth over a greater period as input to get more accurate results but of course this is just another approximation.

Also, there appears to be a bug if you put a large number in the Growth field. For example, if you put 5 (500%) in, it gives you a larger number of BTC than if you put in 4 (400%). You may be overflowing somewhere.

Thanks for this hint, I actually introduced a stupid math bug this morning

Should be fixed now.

Found a 0 division bug. I was hoping that difficulty would never raise Grin

EDIT: Nevermind. I misread the description. I should type 1 if I don't want the difficulty to raise. The bug still exists though...

Yes you got it, just enter '1' into the growth field. Thanks for noticing the division bug, it is now checking for unwanted 0's in the input fields.