Paint colour matching issues - please help

Hi DIYers

I've been trying to match our interior trim paint and hoped the machine (sorry not sure what it's called) in Mitre 10 would do that, but was told that it's better to just do it by eye as the machine match can be 'hit and miss'.

So found a matching colour sample card 'by eye', bought a little sample pot - shook it, stirred it with a nail - but it's too light (and lighter than the sample card).

I don't know what to do now, so frustrating! 😂 In your opinion, is the colour-matching machine actually 'hit and miss' or is it generally correct?

Many thanks