I spent a lovely day in London yesterday with the London Polymer Clay Group (it was a blissful 2 hours on the train from me which I thoroughly enjoyed and I managed to squeeze a flying visit in to the jewellery gallery at the V&;A museum too!). I had already made thickness chips for the 2 machines I have and Nina kindly allowed me to make a set on her Atlas so now I have all 3! Here's the measurements
They will probably be a bit different from machine to machine and possibly even from different sides of a sheet depending on how straight the rollers are but hopefully it's a useful starting point.
So if you want to compare I would say as long as you remember a 1 on an Imperia is about the same as a 2 on an Atlas, 3,4 and 5 are much the same and the thinnest on an Imperia is like a 7 on an Atlas.
(Toni the table won't be visual enough for you - your machine is very close to the atlas measurements)