@hollowayhouse - there's a number of discussions on page counts around these forums, but what it comes down to is the simple fact that there is no such thing as a "page" in an electronic reflowing book format like epub. Adobe have a definition of a "page" being 1024 characters, which is what calibre's reader uses. Other devices and software each can have their own definitions. Since everyone can use different fonts and font sizes there is no one number common across all of them which says how big a page can be. And Adobe's definition is just as "meaningless" a number as Kindle's "location" feature to the average user.
So basically - I would suggest you tell your client they need to get over it
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