I came into a large hatful of indicators made by Mercer Electronics, a
division of Simpson Electric.

These are small (under 2" overall width, mount in a 1.425 x 0.8 "
rectangular hole, and have a meter-style movement driving a cylinder
mounted with axis parallel to the front of the device, rather like a
roll of paper towels. Current drives the cylinder, and a DayGlo red-
orange flag printed on the cylinder changes position. I have three
varieties:

Zero Indicator Cat. # 11338 model 510, 50-0-50 microamps, zero center
The cylinder has two opposing solid-color arrowheads, which are in the
center of the viewing area when no current is applied.

Tuning Meter Cat # 11220 model 510, 0-100 microamps
The cylinder has a single triangular colored area, such that increasing
current increases the red area displayed through the window (leading
edge of the triangle moves to the right, like the speedometer in our
old Pontiac).

Another variety not with me here at work, with 20-10-0 marks along the
top edge of the viewing area and 0-10-20 marks along the bottom edge/
It appeared to be zero-center, and used for tuning or something.

Anyone know anything about these?

--
A computer scientist is someone who, when told to "Go to hell," sees the
"go to," rather than the destination, as harmful.
-- Dr. Roger M. Firestone