The phrase "same unit" means that two or more things are being measured or compared using the same type of measurement. They are in the same category and can be directly compared.
Sentences with «same unit»
It's basically the exact same unit as mine but mine is on the 2nd floor. (biggerpockets.com)
Also, if you ever need to do it again, then you'd have to move back in to the exact same unit. (biggerpockets.com)