When determining whether a Bombarding A.C.
Milliamperes Meter is an RMS Iron-Vane meter or
an inexpensive rectified meter, each type of meter
is easily identified simply by visually looking at it.
On a True RMS Iron-Vane meter (top picture) the
space between the graduations at the lower end
of the scale (left side of the scale) are non-linear.
In other words, they are not the same distance
apart; they are closer together than they are on
the rest of the scale.
On a rectified meter (bottom picture) the space
between the graduations is linear across the entire
scale. In other words, the space between all the
graduations is the same, even at the lower end
of the scale.
The linear scale characteristic of the inexpensive
rectified meter may seem to contradict the accuracy
statement that favors the RMS meter because the scale
of the rectified meter is more readable at the lower end
and therefore more “user friendly” at low readings.
However, in this instance the looks are deceiving. With
the rectified meter what you see (the reading on the scale)
is not what you get (the actual amount of current).