Gerry, Are you sure the gauge doesn't just tell you what datum you are using on your sub scale is? On some aircraft there is a switch that flicks between 1013.2 and QNH but I don't think it can be triggered to change automatically. OTOH if Frank builds his own Altitude Alert gauge then this could be used to trigger the switch operation. It would need two gauges though: Alt Alert gauge could have TA dialled in and then: A:INDICATED ALTITUDE(feet) <= dialled alt should trigger the switch to 1. A:INDICATED ALTITUDE(feet) > dialled alt should trigger the switch to 0. This switch could be an invisible gauge that sets the Barometric Sub Scale to QNH for 1 and 1013.2 for 0. bones -----Original Message----- From: jhb_airlines-bounce@xxxxxxxxxxxxx [mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of FrankTurley@xxxxxxx Sent: 14 November 2006 18:37 To: jhb_airlines@xxxxxxxxxxxxx Subject: [jhb_airlines] Re: A question of altitude In a message dated 14/11/2006 10:32:40 GMT Standard Time, gwinsk@xxxxxxx writes: One of the FS9 panels has just such a gauge. It indicates whether you're on standard or QNH. Gerry Winskill I'd be interested if I knew where to look....... Frank T.