The jaws of a vernier calipers touch the inner wall of calorimeter...

The jaws of a vernier calipers& touch the inner wall means we are measuring inner radius.

Given,

The main scale reading& $MSR = 3 . 48cm$

The Least count of vernier calipers~$LC = 0 . 01cm$

The vernier scale reading~$VSR = 6$

Diameter of the calorimeter measured is,~

$D = MSR + \left(VSR \timesLC\right)$

$D = 3 . 48 + \left(0 . 01 \times6\right) = 3 . 54cm$

There is a negative zero error of~$- 0 . 03cm$. So, the actual diameter of the calorimeter will be,~

$D^{'} = D - zeroerror = 3 . 54 - \left(-0 . 03\right) = 3 . 57cm</p></blockquote>$