Hello Madhu and welcome.

It is really good to see some practical work being done, this is just so important.

The answer to your question lies in understanding where the end corrections come from.

I have drawn a greatly exaggerated error to show the issue.

When you read the bridge you measure from the balance point to what you hope are the ends of the slidewire.

The ends of the slidewire are the points where the heavier copper bus bars are attached (eg soldered) on. They may not be exactly 1 metre apart. I have labelled these points M and N. Also the ends of the ruler may not be exactly aligned with these points.

So I have shown two different errors, alpha and beta, one where the ruler sticks out and the other where the wire sticks out further.

Measurements L1 and L2 are shown and the true lengths for the measurements are L1+a and L2+b.

Of course a is positive and b is negative in this example.

Does this help?