HP-42S with flush and recessed display

[John R]

Yes, the recessed-display models are easier to read, regardless of viewing angle or lighting conditions. I think that both models actually use the same LCD, but that the presence of the extra protective layer in the flush-display model reduces the contrast. I've never had the heart (or the cash) to crack into two HP-42S calculators to verify, though.

A flush-display and a recessed-display HP-42S will also likely have different ROM versions. This difference is not inherently related to the display or to a common underlying factor, but simply reflects the fact that units with later manufacture (i.e., those with the recessed display) may have newer ROMs.