The Millen grid dipper was never a calibrated ,or accurate device, to
get an accurate reading ,tune a receiver to the desired frequency and
set the dipper to the receiver ,You will be anble to get "in the ball
park" Good Luck W4PQW

Hmmmn. Never calibrated?

I bought my 90651 new in 1955. It was
considered the best GDO *because* of
its good calibration. The accuracy was
very good for a time when frequency
counters were laboratory curiosities.

73, John - K6QQ