Gauges

[olderndirt 1]

Some of the primary flight instruments - airspeed and altimeter - are intermittently twitchy, 10-20 kts or 100 ft but, by and large, a fine rendition.

[Herman 903]

Do you have turbulence turned in in your weather settings. It can cause this.

Unless you need it for soaring, I suggest leaving it off. It's far from realisitc.

[Mathijs Kok 30746]

Some of the primary flight instruments - airspeed and altimeter - are intermittently twitchy, 10-20 kts or 100 ft but, by and large, a fine rendition.

Check if this is caused by weather (some weather add-ons create rather unstable winds). Also note that we made all needles more realistic than the standard FSX ones, they should twitch all the time.