I had an HP28c ( https://www.hpmuseum.org/hp28c.htm https://www.hpmuseum.org/hp28c.htm ) that saw me through high-school calculus and undergraduate work. In it

I had an HP28c ( https://www.hpmuseum.org/hp28c.htm https://www.hpmuseum.org/hp28c.htm ) that saw me through high-school calculus and undergraduate work. In it's day, it was a revolutionary product. I never got to play with the data sharing stuff, since none of my classmates had such an expensive or geeky piece of kit (I got mine used, but it was still expensive).