My old trusty Casio fx-61F “Electric formula 27” calculator is still going strong and gets regular use. It was bought in a sale from Maplin Electronics UK, some time in the 90s from a bargain bin as I recall. Why is it so special? Its a calculator specifically designed for electrical and electronic engineering. I don’t know of any other calculator specifically designed for this type of engineering.
It does what I want, how I want it to and even feels good in the hand. Over the years it’s taken a bit of a battering so I finally managed to get another one from eBay at a reasonable price. I say reasonable but I mean it cost nearly 3 times what I paid in the original 1990s purchase sale!
I used it on my Open University Electronics course (T202) in the mid 90s coming to rely on it for some of the formula used. Then forgot how to use some of the key calculator formula in the exam which caused a bit of an issue! Lesson #274836 always know how to do it with pen and paper😀
The solar panel works impressively well to this day. The Engineering function is always useful for reducing those overly long numbers to something more manageable. I have a picture of the insides somewhere, I’ll post them when I find them.