Thanks a lot for all your help. will confirm with tenant

if it's really 180V coming out of power outlet, because he has no basic knowledgement about electricity, or I will go there again check the voltage again. if it's really 180V, will call ultility company to check.

it just doesn't make sense to me that why the rest of staff like refrigerator, lights etc in the house works fine while an instrument display shows 180V (he claims), and he suspect there is something wrong with the electricity system in the whole house.