how would you identify a standard metre scale?

Weight and measurement department puts its seal on it to make sure that the scales and weights are standard. That is how you know their accuracy.

It's come under the international system of unit.Approved as S.I. the modern form of unit.It compresses the system of unit of measurement built around 7 base unit. the standard published in 1960 as based on c.m,Kg.,second meter system. etc.
I.S. used by major professions and cod organisations.To measure the length, height and depth we use the metric unit scale.

A standard metre scale is often sealed by the govt. authorities to ensure its accuracy.

World standard for measurement follows Metric system. The standards are defined by International System of Units in which you can identify a standard metre scale.
For details : http://en.wikipedia.org/wiki/International_System_of_Units

When we are seeing we can identify I think. Other scales are very different.

Only seal of measurement department is proof of standard measurment. But in Indian more over person are not using standard measurement tools. here people use piece of stone or some iron piece to weight.

There is some precision which is considered while manufacturing a metric scale so I guess they come as identified standard metric scale.

You can have a standard meter scale calibrated which you can compare with the scale you want to check.

By using a Varniercaliper scale we can calculate it easily without any mistake.

This is a good question.
I think Varniercaliper can be used to identify a standard metre scale.

The metric system is an international decimalised system of measurement that was originally based on the mètre des archives and the kilogramme des archives introduced by France in 1799.