I tend not to be greatly interested in aviation related calculations I can't do in my head whilst instrument flying with one hand and 90% of available brain space pre-occupied with the flying! It's all very well doing these bizarre calculations, but the flying and keeping a lookout come first, and frankly, converting gradients to fpm at current groundspeed is one of those esoteric maths problems there is no room for!
Still shouldn't have mixed up my units there though. Must be getting old.