I recommend to use "ladder" technique instead of simple repeats, because it adjusts itself, so no need for app, spreadsheet, or personal trainer to calculate proper weights and number of repeats, moreover, it has lower risk of injure.

Start with x repeats, then count to 20, do x•2, count to 20, do x•3, ..., until you tired, e.g. x•5, count to 100, then do x•4, count to 20, do x•3, count to 20, do x•2, count to 20, do x repeats in row. X can be 1, 2, 3, 4, 5, etc., e.g. 5, sp, 10, sp, 15, sp, 20, lp, 15, sp, 10, sp, 5, lp, an another exercise...

Important NOTE: Each of downslope repeats must feel like top repeat, i.e. you should be equally tired for X•N, count to 100, X•N-1, count to 20, X•N-2, and so on. If you are not tired, then increase X or weight.