The calculations are very helpful when the master nodes are not listed on a master node website yet or when they are sync or something is wrong with the wallet.
Also good if you want o use btc instead of fiat currency.
This return on investment(ROI) is based on the assumption that all parameters are going to be the same
Unfortunately, the assumption is very weak.
price is going to be volatile even if you analyzed DASH.
people is going to buy masternodes too so in the next days there will be more masternodes so the daily frequency payment is goin to be lower every day.