HP rpn calculators are the best. I have 2 HP12cs on my desk that have accompanied me through my career in finance and still get used every time I want to calculate anything and don't want to crack out excel. To give you an idea how durable these things are, mine are later models using the inferior battery tech and poorer quality fabrication and are still running on their original batteries after 20 years of near daily use.

I fondly remember programming my dad's HP calculator[1] to do various important chemical engineering things when I was 10 or so.

There is a famous story about a zookeeper who was using an HP12C to calculate ratios for different ingredients and accidentally dropped it into the feed. According to the story it passed through the digestive tract of a hippo and was still able to calculate the yield to maturity of a bond after cleaning[2].

[1] Looking at old photos I think his was a 29C or similar. [2] Recounted here https://www.hpmuseum.org/hp12c.htm