Factory Built Heath EU-80A Voltage Reference Source

Description

Factory-built (not a kit) Heath EU-80A DC Voltage Reference.
This unit is basically a 10 V DC source with a nominal 3-digit precision, packaged together with a decade attenuator bank.  You can dial in any voltage from 1.00 mV to 10.00 V DC, positive or negative polarity, plus a push-button zero output.  There are also options for adding or subtracting an external input voltage via an extra set of terminals.
As I do not have a copy of the manual, I do not fully understand all of the functions beyond the basic dial-in DC voltage reference function.  I do, however, have a
printed copy of the calibration instructions
, which I will include.
I have checked the basic operating functions, including + and - voltages from 1 mV through 10 V and found them to mostly fall within the expected values, except for the lowest mV range, using a Fluke 189 DVM.  I do not have a high-accuracy bench meter, so I have not attempted to adjust the calibration.  As there is no calibration tag or sticker attached, you will probably want to have this unit lab calibrated in order to ensure up-to-spec performance.
The only other issue that I am aware of is that the power cord is damaged (and very crudely repaired) approximately 4 inches from the plug.  If I intended to keep this unit, I would probably shorten the cord and install a new 3-pin plug.