Neal, N/cm to lb/in is simply a case of multiplying the N/cm number by 0.571401
If you do that with the AE whites in your example you get 3.11lb/in ... now if the displacement on your gauge was only an effective 95mm then that would be spot on.
By effective displacement I mean that it is entirely possible that the first few mm are just "settling" everything down and not actually compressing the spring, this will be amplified if there is any slop in the plunger at all or the springs aren't dead straight.
To get around this I suggest you pre-compress the spring by a few mm (5mm would be fine) and make sure that when you displace your gauges plunger by 1cm it achieves the full 1cm of travel.
That way the numbers will be much more consistent.
When I tested AE springs on my work's tensile/compressive tester (£50k worth) they were with in 1%
Hope that helps
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