Of note on the air core gauges. There is no return spring or direct physical connection to the zero point on the instrument. As such, when power is removed (ie the vehicle is turned off), it will not always return to zero. This is consistent throughout all of our electronic gauges and allows for an incredibly responsive and fast pointer movement (air core tachs are capable of moving from 0 to 10k rpm in 333 milliseconds). It is not uncommon to see a new gauge in the box where the indicator is not zeroed out. This is totally normal and not indicative of any failure. Because these types of gauges rely heavily on accurate resistance measurements of the sending unit, a good ground is imperative for the best possible results during installation. The gauge will only be as accurate as its ground is good. We recommend an engine block ground point above all else. A SSE gauge with an inadequate gauge ground will oftentimes read higher than it should, particularly with temperature gauges as they operate over a very wide resistance scale. The sending units SSE gauges utilize are “self grounding”, meaning they find their path to ground through the threads or the body of the sending unit. This design does not play well with Teflon tape on the threads as it will impede the path to ground and will often manifest as a sluggish response or a gauge that reads lower than it should. A small dab of liquid Teflon will provide insurance against leaks without the potential for erroneous readings. The sending units do utilize a tapered pipe thread, so leaks are not typically a problem, even without any thread compound whatsoever.