How do you measure a TV screen in cm

Question

I just bought a 72cm TV and I measured up down corner to corner

and the closest number to 72cm is {67cm LB to RT}

unless their is some formula?

It is a flat screen TV

Answer 1

You measure it from left corner to right corner and that is the size.

In inches that tv is 29"

Answer 2

I was told you measure from the bottom left hand corner to top right hand corner. Maybe they count the casing around the TV?

Answer 3

you measure it diagonally