Identification of seat post?

[DavidB1978]

Hi,
Can anyone more experienced tell me if this seat post is 20mm offset or zero offset? I appreciate this is an odd question, and perhaps a difficult one but help would be appreciated.
I believe its a Ritchey.

Thanks,
David.

 

[black'n'yellow]

it isn't zero offset, so if the other choice is 20mm then it must be that...