D-100 Altitude Adjustment

[uk_figs]

System has been working well since 2008 but recently my altitude readout  has been off by about 100 feet from my flying buddies (at the same baro setting). I read the ALTADJ section in the manual but it does not say specifically how to do this, do I set 29.92 with the HS34 and adjust the reading to match my airport field elevation. Is this something I should expect to drift over time?
No other changes have been made to the pitot static system.
Thanks

 

[robertc]

My experience is to make sure it's warmed up. (Altitude reading stabilized) set the baro to the current reported value, then set the offset to the field elevation. Hope this helps. Bob

 

[Dynon]

Yep, what Bob said. If you're seeing more variation from day to day, we'd want to see your EFIS here.