Friend of mine in IA has been using this tack on his VW powered airplane and likes it. I made an aluminum plate to mount it in a 3 1/8" instrument hole. Also a bracket to mount the sensor behind the prop flange on my C-85 and Aircraft Spruce sells a cap to cover the tack drive on the accessory case of the engine. Range from 0--9999 rpm. Can be powered by the 12V electrical system or like my friend uses, a 9V battery mounted behind the panel. I hooked it up to a 9V battery for the picture. You will be saving almost a pound over the use of a mechanical tack and cable. Not counting the money. Price is $10.88 including shipping. http://www.ebay.com/itm/Blue-4-Digi...199067?hash=item1a11c3df5b:g:E6EAAOSwxH1UFwfB BTW-- Notice the use of an blue aluminum breather elbow on the Cont engine. Saved over 1/2 LB over the stock brass elbow.