### Units of dtauda in CAMB

Posted:

**July 09 2022**Hi!

In CAMB, the module equations.f90 has the dtauda function. I have found in the CAMB Notes that "everything is in conformal time and units of megaparsecs", but cannot find further information, and I do not know exactly how to take this. Does this imply that everything is in natural units, with the chosen reference unit being megaparsecs? Or are just distances measured in megaparsecs, and times (eg. tau in dtauda) measured in units of conformal time, rather than for example seconds or years? I really just want to know the units of tau.

Thank you!

In CAMB, the module equations.f90 has the dtauda function. I have found in the CAMB Notes that "everything is in conformal time and units of megaparsecs", but cannot find further information, and I do not know exactly how to take this. Does this imply that everything is in natural units, with the chosen reference unit being megaparsecs? Or are just distances measured in megaparsecs, and times (eg. tau in dtauda) measured in units of conformal time, rather than for example seconds or years? I really just want to know the units of tau.

Thank you!