The Mk V E-Meter as originally used in the CofS suffers from several major faults. The major trouble is that it is insufficiently sensitive to pick up reads on OT level 5 and above. At the higher levels one is often dealing with small reads sometimes through a fast moving needle.
The CofS attempted to produce a better meter in the Mk VI. While the quality of some parts was improved the essential circuit was very similar to the Mk V. The major change was in the meter movement. My own tests indicate that the Mk VI is actually less sensitive than the Mk V. The Mark VII is a much improved product that uses a superior quality of movement and picks up many more reads. Unfortunately the CofS appears to have an arbitrary in the design spec. The Mk VII movement, in common with earlier models does not come to rest after a read for several seconds. It actually swings 8-10 times before settling. This uncontrolled movement can obscure and confuse reads. I have recently had a meter movement produced that does not swing about after a read. An increased torque in the coil produces a faster needle response to changes in the pc. Using a device that I built a pc can be connected to 2 meters simultaneously. Comparisons using it show reads on the improved design not present on any CofS meter.
I have written up data on the E-Meter with full circuitry and specification: E-Meter Circuit