Two different examples of "2668-B PC" (manufactured circa 1976, for the 8 bit, analog-to-digital
converter by DATEL Systems, Inc., ADC-89A8B) show different values for four resistors.
(These boards had been encapsulated in black diallyl phthalate casements by the
manufacturer, possibly in order to conceal the design (from competitors) and perhaps
also to maintain more uniform temperature among the components. Some
type of semi-liquid foam had also been placed over all of the component side of
both boards before they were sealed. This had to be washed off and wiped with
a Q-tip in order to show the circuitry).
Board example, A: