Screw Gauge!

Least count of screw gauge $=0.01~mm$

Reading is noted as

$\text{Main scale reading+(circular scale reading)*least count}$

let us take $zero~error$ to be positive and be $x$

$\text{Actual reading =Observed reading -zero error}$

reading from diagram 1

$2+(12-x)\times 10^{-2}~mm$ .............................. $(1)$

reading from diagram 2

$4+(10-x)\times 10^{-2}~mm$ ................................. $(2)$

As the rods are identical so reading of two rods must be equal

$2\times (1)=(2)$

$2(12-x)=(10-x)$

$x=14$

since $x$ comes out to be positive so our assumption of taking zero error positive is correct,

so zero error $x=+0.14~mm$