Most people choose a TV stand by looking at it. They find one that suits the room, put the TV on top, and never think about the height again, until three weeks of film nights in they notice a faint ache at the base of the neck and cannot work out where it came from. It came from the height.
A screen is one of the few things in your home you look at for hours without moving. Get the height wrong and your body quietly pays for it every evening. Get it right and you stop noticing the stand entirely, which is the whole point of a good one.

The only rule that matters: start from your eyes
Forget the stand for a second and think about your face. When you are sitting normally on your sofa, relaxed, not perched forward, the centre of the screen wants to land at roughly eye level or a touch below. Your neck is happiest looking straight ahead or gently down, the way it does when you read. It is not happy tilted up at the ceiling.
That single rule quietly decides the height for you, and for most living rooms the answer sits lower than people expect. Sofas are low. Eye level from a sofa is low. So the screen, and the thing holding it, should be low too.
This is the reasoning behind a Vislund stand sitting close to the floor. It is not a styling quirk. A low profile keeps the picture where your eyes already are instead of asking your neck to climb up to meet it.
Measure it in five minutes, before you buy anything
You do not need a diagram, just a tape measure and the actual seat you actually watch from, not a kitchen chair standing in for it.
Sit down properly, the way you would for a two-hour film. Have someone hold the tape at the height of your eyes, and note that number from the floor. That height is where the centre of your screen wants to be. From there it is simple arithmetic: the middle of the screen should hit that mark, so work backwards to where the bottom edge of the TV needs to sit, and that tells you the height you have to play with for the stand and mount together.
Do not forget the stand adds its own height
The classic mistake is measuring for the screen and forgetting the furniture underneath it. Whatever number you land on, the legs and base lift the TV up before the screen even starts. Factor that in, or you will end up higher than you planned.
On the mounting side there is less to worry about. Vislund stands take VESA patterns from 200x200 up to 600x400mm, which covers the large majority of TVs from 42 to 75 inches, so the hardware almost never dictates your height. Your room does. The distance to the sofa, the height of the seat, where your eyes land.
Measure twice, decide once. It costs you five minutes now against a small nightly annoyance you would otherwise learn to live with and never quite fix.

