This is not promoting an advert - just look and see! There is a 'clip on' ammeter for sale on eBay and I can't imagine how it works. It claims to work by clipping it round a cable and the scale shows +/- 30A DC. I spent good money on a Hall Effect clamp meter when it looks like I could have spent a whole lot less on one of these. Plus, it doesn't seem to need a battery. I guess the error could be in the "DC" claim. Perhaps you have to see how far the needle moves, momentarily at switch on??