A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2019 Nov 20, 16:13 -0800
The Casio fx260 solar (the II model is in production now and has some aesthetic improvements but no other changes) sells for about $8 at retail stores in the US. That's about £6 at current exchange rates. They may not market this under the same name in Europe. Look for the equivalent.
This calculator has no battery. It has some capacitance to it (cover the solar cells with your hand and the display will stay lit for ten seconds minimum), and some sources may refer to this as a "battery", but it's not something that would ever be replaced. I have had a few of these calculators for over ten years. It is purely solar-powered and works at quite low light levels. If you hold it close to a candle in the middle of the night, you can get it to do all the spherical trigonometry you might desire at 0-dark-30. Yes, I have tried this.
As for the threat of salt water, I have tried that, too! It must have been a while since I have posted about this topic since I have described my experiments in "calculator torture" quite a few times in NavList posts. These calculators are indestructible, like bricks --floating bricks. Drop one in tropical-temperature salt water, and you'll immediately notice that they don't sink for a long time. When an fx260 does go under, if you pull it out, shake the water out, and let it dry, it's back in business in no time. These calculators also survive substantial static electric shocks quite well.
By the way, if you're an Android user, you can try out my fx260 emulator under the listing for my "Modern Celestial" class here: http://www.reednavigation.com/mod-class/. You have to enable third-party app downloads, temporarily. There's nothing remarkable about the app as a calculator. This is just something for training purposes (and for students who attend my class who don't want to spend $8).