2nd Harmonic Grade test module

I need some help identifying something I bought at an auction.  In with
a bunch of older Modicon PLC modules, I found four new modules that are
made for a rack and "2nd Harmonic Grade" is printed on the front.
There is a 10vDC meter, on/off switch, "ACPT" LED, "REJ" LED,
J1 jack, J2 jack, gnd jack, and a Knobpot Bourns "Level" adjustment
knob with an adjustable clock type setting under the top of the knob.
The circuit board is marked with the number 0039-8416-9-006-01.  This
did not come up as a NSN.  However, this is at least 15 years old so it
could be obsolete.  The circuit board has a logo that looks like a
backward "K" joined to a lower case "b".   Other than the
electronic component labels, there are no other markings or name
brands.  It has 22 wide contacts in back of which 17 are in use.  The
contacts are side by side on a part of the circuit board for a blade (?
term) contact.  Here is a link to some pictures of this module.
http://www.ardnet.com/3sands/2ndHarmonic.htm

I am not trying to sell them here, but I would like to know enough
about this to put it on eBay for a little extra Christmas money.  I
have found out what the 2nd harmonic is and I am guessing that this
will test certain electric or electronic devices.  I don't know what
it is called or what it tests.  Any info will be greatly appreciated.
A website for the product would make me your friend forever.  Thanks in
advance for any info you can provide.
John Sands
John@ardnet.com