{It took a lot of fussing around.}

Richard,
thanks for that. The gang at PocketFMS swears up and down it can't be
done so I assumed it was not possible.

Is this fussing that can be explained, or is it beyond us mortals? I
personally could be happy with landscape.

mounts.
I suspect that using the suction cup to stick the 310 to the glass
face of the altimeter won't get much approval. The ball and socket
part of the mount ends in a 1/2" flat that meets the flat of a
tightening knob. If the suction cup support arm was cut away a small
hole could be drilled into flat stock (or the panel itself)and the 310
mount could be attached by by using the tightening knob as a mounting
bolt.