I found 2 of these in the road in a ziplock bag. Both work. They have to be 40 years old. I had one which was given to me by a trucker and I bought a 15C. These cost as much as a laptop would today. Reverse Polish notation kicks your brain into a higher gear and some calculations are faster. I’m keeping them. They are still sold and I don’t blame business men for buying them I only like to master one computer at a time.
I have owned at least a half a dozen HP calculators with RPN, and still have some today. Nice find!
I have a HP 20(?) I bought for chemistry in undergrad and kept it even though I haven’t used it in years due it being so good.
My go-to calculator in business school and life in general was/is the HP 19B.
Love it. Its simple yet customizable.