DC Millivolt Reference Source E100RC

The precision DC Voltage Standard Source is a highly versatile reference source, designed to meet the needs of computer systems, production line testing, automated calibration, and standards laboratories.

The instruments have a specified accuracy, and are traceable through a bank of saturated standard cells to the U. S. National Institute of Standards and Technology.

They can be used for calibration of digital voltmeters, analog meters, semiconductor analyzing systems, analog references for computers, analog-to-digital converters, telemetry and data acquisition systems, and where ever a stable source is required.

Output
Range 1: ±10 Vdc +10%  over-ranging; Range 2: ±100 mV dc +10% over-ranging

Resolution
Range 1: 100 µV (10 ppm) 5 decades; Range 2: 1 µV (10 ppm) 5 decades

Accuracy
Range 1: ±0.005% of setting +50 µV; Range 2 ±0.01% of setting +5 µV

Stability
1 hour ±0.0005%;8 hours ±0.0010%; 1 year ±0.0025% of range +5 µV

Here you find 3 models, 3 with images and 0 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from Electronic Development Corp. (EDC); Boston, MA