I did consider the SoC, and cannot comment on noise. However, you will note at the higher impedance the % deviation from average is 9.4 while at the lower end somewhere in the order of 60%. 

We have a 1741 + but it was not on site.

Previous result recorded by me on a different instrument 5 years ago was 1.58x2. 

Will commence experimenting at the training centre during 2391 where we have access to a board close to the intake.

lyledunn said:

at the higher impedance the % deviation from average is 9.4 while at the lower end somewhere in the order of 60%. 

Or a difference in range of 0.18 Ω, giving a deviation of ± 0.9 Ω from median.

lyledunn said:

at the higher impedance the % deviation from average is 9.4 while at the lower end somewhere in the order of 60%. 

Or a difference in range of 0.18 Ω, giving a deviation of ± 0.9 Ω from the centre of the range.

I guess what this experiment illustrates is that:

• Loop impedance testers are not accurate at low values of Zs / high values of Ipf (which we already know) - what we don't know I guess is what the real reading is.
• 3 instruments is not a large enough population to gather statistics in measurement uncertainty.

lyledunn said:

at the higher impedance the % deviation from average is 9.4 while at the lower end somewhere in the order of 60%. 

Or a difference in range of 0.18 Ω, giving a deviation of ± 0.9 Ω from the centre of the range.

I guess what this experiment illustrates is that:

• Loop impedance testers are not accurate at low values of Zs / high values of Ipf (which we already know) - what we don't know I guess is what the real reading is.
• 3 instruments is not a large enough population to gather statistics in measurement uncertainty.