  We study thermodynamics of SU(3) gauge theory at fixed scales on the lattice,
where we vary temperature by changing the temporal lattice size
N_t=(Ta_t)^{-1}. In the fixed scale approach, finite temperature simulations
are performed on common lattice spacings and spatial volumes. Consequently, we
can isolate thermal effects in observables from other uncertainties, such as
lattice artifact, renormalization factor, and spatial volume effect.
Furthermore, in the EOS calculations, the fixed scale approach is able to
reduce computational costs for zero temperature subtraction and parameter
search to find lines of constant physics, which are demanding in full QCD
simulations. As a test of the approach, we study the thermodynamics of the
SU(3) gauge theory on isotropic and anisotropic lattices. In addition to the
equation of state, we calculate the critical temperature and the static quark
free energy at a fixed scale.
