I've been experimenting with a 'power-supply' version of my buck converter kitset. It features 10k pot's to adjust voltage & current however, on their own they are too sensitive. It's so easy to over or undershoot your target voltage or current. Adding an additional 1k pot in series to the other 10k pot, gives the user the option for fine & coarse adjustment to precisely hone in on your target voltage or current. This idea is nothing new in fact, dual fine & coarse pots are often found on commercial power supplies.