zstar calculation in CAMB

[prakharbansal16]

I was trying to understand how zstar is being calculated in CAMB. After digging a lil bit, I found out that CAMB uses the equation given in the paper Hu & Sugiyama (https://arxiv.org/pdf/astro-ph/9510117) to evaluate zstar. However when I explicitly checked the value of zstar using the expression above and using the get_derived_params()['zstar'] command, the two values don't match. What could be the reason for the same?

[cmbant]

It uses the definitions of the Planck papers (e.g. see Planck 2013 parameters)