Not talking about the latest sight glass/fill plug stuff, but the old traditional dipstick. I rarely feel like I get an accurate reading with hot idle as fluid from the tube/splash/what ever makes for a hard read. With the older transmissions it didn't seem like they were all that fussy as 'close' was good enough, but some of the later do seem to 'want' levels within a narrower range. With some transmissions I've found that cold and off give about the same readings as at idle-others not. The latest is just a fluid R+R on my 'winter beater' '05 Elantra and it wants OE fluid 'just right there' or shifts aren't as they should be=all a pain in the wahzoo!