<font face="Verdana, Arial, Helvetica" size="2">Is the VSI acurate at Altitude ? Yes, the vsi Basically measures a leak rate difference between two chambers of a bellow, thus not sensitive to altitude.</font>
Sorry
Doc but if the pressure difference between the two chambers is only half what was at ground level the needle will only deflect half as much. You haven't explained what compensates for the fact that pressure does not decline at 1 mb per 30 feet at jet altitudes.
At least I don't think it does.