Comment by e3pi

Free 42S is my favorite phone app. I've the original 42S manual PDF -- not easy to find -- their `charity' pay-wall.

~35MB Download: original HP 42S 358pp manual: e3pi.org

I've many HP rpn's, Free 42S is better at everything, except keys haptic satisfaction.

If you're voyager/landscape 10C 11C 12C 15C 16C centric, rotate phone: rot90:HP-42S <--> HP-42C

yes, ballistically-black ruggedized Otterbox-ed, cost $0.00.