Interchange Error Issue in high resistance meter /Interchange Error Issue on Pre

[email_removed_by_admin]

I work with precision resistance measurement instruments based on DC comparator (DCC) bridges, specifically a unit similar to the Measurements International 6010D.

I’ve been encountering an issue where the interchange error in is around 0.1 ppm in one unit limit is +-0.02 . I tested another similar unit, and its interchange error is around -+0.2 ppm, which is also higher than expected.

Here are my questions:

What could cause interchange error to consistently remain high in such systems ?
Could this be related to internal components (e.g., magnetic core, capacitors) or external factors (e.g., lead connections, environmental conditions)?
What are the best troubleshooting steps to minimize interchange error and achieve more consistent results?
Any insights would be greatly appreciated!

Thanks in advance!