"Travis Marlatte" wrote:
You seem to be suggesting that when flying VFR above 3000', we have an
obligation to fly specific altitudes within some tolerence and, therefore,
need to have an accurate means of determining our altitude. That is
certainly not the case. Prudent, yes. Required, no.

I would consider the following to be an "obligation":


*91.159***VFR cruising altitude or flight level.

Except while holding in a holding pattern of 2 minutes or less, or while
turning, each person operating an aircraft under VFR in level cruising
flight more than 3,000 feet above the surface shall maintain the
appropriate altitude or flight level prescribed below, unless otherwise
authorized by ATC:

(a) When operating below 18,000 feet MSL and‹

(1) On a magnetic course of zero degrees through 179 degrees, any odd
thousand foot MSL altitude +500 feet (such as 3,500, 5,500, or 7,500); or

(2) On a magnetic course of 180 degrees through 359 degrees, any even
thousand foot MSL altitude +500 feet (such as 4,500, 6,500, or 8,500).

(b) When operating above 18,000 feet MSL, maintain the altitude or flight
level assigned by ATC.