measuring a valve guide for wear?

[karoshi]

Haynes tells me that the width of the inlet valve guides tolerance in my engine is just over 5.5mm and that while i'm replacing the valves I should measure the width of the guide at three points vertically along the guide..

I can't do this with a bore micrometer, is there a specific tool for doing this that i'm not aware of?

Bakcup plan, stick a new valve into the guide and see how wobbly it is I guess?
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