  Unimodular Gravity (UG) is a restricted version of General Relativity (GR) in
which the determinant of the metric is a fixed function and the field equations
are given by the trace-free part of the full Einstein equations. The background
equations in UG and GR are identical. It was recently claimed that, the first
order contribution in the temperature fluctuation of the Cosmic Microwave
Background (CMB) in UG is different from GR. In this work, we calculate the
first order perturbation equations in UG and show that the Sachs-Wolfe effect
in UG, in terms of gauge invariant variables, is identical to GR. We also show
that the second order perturbation equation of Mukhnanov-Sasaki variable in UG,
is identical to GR. The only difference comes from the gauge choices due the
constraint on the metric determinant. Hence, UG and GR are identical and
indistinguishable in CMB data on large scales.
