HP Rotate and Click keys

Selected models on the HP Calculators lineup have special keyboard contacts that give positive "tactile feedback" so you know the button has been depressed. The rotating design ensures contact even when pressed off-center, which prevents missed input strokes.

HP calculators HP 39g+, HP 39gs, HP 40gs, HP 48gII, HP 49g+, HP 50g, HP10bII, HP 12c, HP 12c Platinum, HP 12c, HP 17bII+, HP 33s and HP 35s have the Rotate and Click keys.