When sizing a part (especially tanks), it would be handy to know what the specs of that part are. I do know you can get this info from the part shape tool (handy but not obvious). A lot of the time I am just wanting to make a tank 5m wide or something, but I don't know how wide that is until I go and measure it after the fact.
Maybe display a number next to the arrow while changing the size of anything, not the part radius because that can mess with non cylindrical shapes.