I've used this stir plate twice now, with both the included 1" magnet and an optional 2" magnet.With 3L liquid inside a 5L E. flask and the 1" magnet there was no problem adjusting the speed enough to create a nice whirlpool.When i tried the same 3L liquid inside a 5L E. flask and a 2" magnet, again had no problem creating the required whirlpool, BUT unless the speed is very slowly increased, the magnet would be thrown to the edge of the E. flask.In general, as the speed dial is adjusted clockwise, the magnet speed increases, BUT between about 10 o-clock and 11 o-clock position there was little if any speed increase which suggests to me that the internal potentiometer is not 100%. I'll watch that this behavior does not worsen.