Jim Weir wrote:

The sensor I have reads two axes, and my hit is that fore-aft is the least
interesting vibration mode of the engine. The question is whether to have a
two-channel meter (which complexes up both the design AND the panel space), a
single meter switchable between lateral and vertical) or a single meter with the
two axes summed together.

My take is that summing the two axes would be perfectly acceptable. I agree that
fore-and-aft is unlikely to produce any interesting results. In fact, I'd bet that
any mechanical problem would show up as an increase in lateral vibration. Vertical
vibration would tend to occur only just before things come apart, IMO.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.