half-tempo vs full-tempo loss

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LionMind22

Hi guys,

 

I hear GM-commentators often say that "this move lost a tempo" and other times "this move lost half a tempo". Can you explain the difference using an example?

Isn't one lost move always a full tempo? Can it be half a tempo?  

 

Thanks!

 

urk
Losing half a tempo means you could have chosen a different move?