Xacc, yacc, zacc info

Hi
i had recently start a project and i was tring to implement a controller by python;
i was thinking to use the xacc, yacc, zacc data that can by export by the ardusub computer, but i have some question:
what are there mesurement units? m/s?
and they need a offset? because i see that when the rov is still i reed values different of 0