how does difficulty affect mining for btc and eth. is it 1 is to 1?

I'm trying to calculate the NPV for a miner..

as the title says, if difficulty increases in a straight line over a year, how does that translate to the number of coins mined?

for example, if over the past year, difficulty increased 30%, does that mean that I mine 30% less coins in the same time span?

Submitted August 23, 2017 at 05:03AM by heyarn http://bit.ly/2wvUdeh