Um, Clamity, back when a US magazine, probably Popular Mechanix, published a design for a DIY meter. I know because one of my friends made one. I now have it, I'm not sure it works. If you want it and I can find it, its yours for postage. IIRC, there's a copy of the article with it. If I can find it. Send me a PM if you want it. And don't tell me you'd rather spend more than the cost of a new one to have one you made yourself.