You should leave the conversion % increase at 0 because if the mining equipment isn't going to ROI in BTC terms then what is the point of going through the trouble of mining when you could have just bought BTC.
That is what I'm trying to figure out... if you can get ROI. If you're using a calculator that calculates your return over several months, I would assume you need to include the change in BTC currency value over that period.
For instance, if I spend $6k, then spend 6 months mining, those coins earned in 6 months aren't still worth the $213 (or whatever current value is today)... if they're worth more, that could help your ROI.
I'll give this a shot:
Imagine that the miner you bought is a *dollar printing machine*, which you buy with *dollars*.
When trying to figure out if it makes sense to buy this gizmo, do you need to know how *the dollar* price will change relative to the yen?
Hopefully, you've answered "No. All i need to do is know how many dollars this gizmo will print in its lifetime, and how much i have to pay for it. If I pay less than it makes, I win. If not, then no deal."
Now substitute BTC for dollar.
Potip: If you think bitcoin's going up in price, buy bitcoin with the money you would have spent on the mining gear FTW.
