I recently lost an older F1 chrono (blue) and am trying to replace it on ebay. I don't have the original paperwork and am confused by some of model number information found on the back of the case. I have noted the there seem to be two designations: CR1210-R0 (sometimes with a serial number sometimes not)and 373.513. Both watches look almost identical. Is there a difference? Is one authentic and the other fake? Can anyone help me?