I ran this picture (also seen in this post) by the hpmuseum.org forum members:

Unknown calculator

Unknown "calculator"

There are many calculator collectors in there and I figured one of them might be able to identify the “calculator”. It seems it might not even be a calculator after all, contrary to what the NASA caption says. Member Joerg surmised that it might be a data collector such as those manufactured by Telxon:

Telxon PTC-710

Telxon PTC-710

The resemblance and design definitely are striking and I consider the “case” closed. An additional tidbit of information about the company Telxon which may be relevant to this matter was found on this webpage:

Telxon was started in Texas in 1969 as Electronic Laboratories, Inc. by engineers who developed data recording devices for NASA and the FAA, the company was a pioneer in the mobile information systems industry.