Still using my HP-15C from 1985. RPN is the only way to go.
And there are people who simply can’t stand it. Of course the hand calculator has gone the way of the dodo bird by now but I stick to it. I still have my sliderule as well but don’t use it except the little one in the truck I use to check my gas mileage though I mostly do it in my head. Still don’t trust that computer in the truck.