I think janrein's case is spot-on but I'd like to add a small rider. If you only have one instrument, it is important to know the one you have is not telling porkies. An A/H running on a flat(ish) battery is as much use at tits on a frog. However, a T&S will still give relative information when run on a low voltage. It won't be accurate but you will know if you are turning or not. And remember the reason it is fitted? It is the back-up for getting back to VFR not the key to going IMC.
PM
Last edited by Piltdown Man; 3rd Sep 2010 at 15:40.
Reason: Spellung