[Yahya A.Sharif (OP)]

You need to understand that g in elementary physics is a number 9.8 m/s² before you reply

LOL
It's not a number.
It's a value.
You can tell because it has units.

And it's not constant.
https://web.archive.org/web/20110605043202/http://ethesis.helsinki.fi/julkaisut/mat/fysik/vk/virtanen/studieso.pdf

g on earth's surface is constant 9.8 m/s² it is usual for measurements on earth's surface.

[Bored chemist]

g on earth's surface is constant 9.8 m/s²

No
It really is not.
Try reading the paper I cited- and then try understanding it.

[Bored chemist]

If it was a constant  then nobody would set up  a page for calculating it.
https://www.sensorsone.com/local-gravity-calculator/

[Yahya A.Sharif (OP)]

LOL
Do you think your doctor will ask you what was your weight  in the country you have been to?
Weight with constant g is used in medicine it is science.

So this is an important definition that I would like to repeat:
The definition of weight is the gravity force mg on the scale by your body mass m where the only forces on the scale are gravity force by your body and the  normal force by the scale, if forces change as in the video then it is not weight. Weight is a standard of how a human  loses or gains body mass m, if g is constant weight mg can be equivalent to mass m the scale shows the mass m in kilograms

[Bored chemist]

Do you think your doctor will ask you what was your weight  in the country you have been to?

My doctor knows that a glass of water before I talked to him makes more difference.
But, if you are trying to introduce a new idea into physics, you have to do things properly.

Why don't you learn science?

The definition of weight is the gravity force mg on the scale by your body mass m where the only forces on the scale are gravity force by your body and the  normal force by the scale,

OK so we know that's not a constant- you might think about whether it depends on if the sun is overhead pulling up.