Hi, as explained more thoroughly in the Cal 11 post pointed at by Mark, in that period Lemania was a part shareholder of the Heuer company.
A number of watches - especially chronographs - of that period in fact housed Lemania 5100 movements - either completely or derived: both the PVD and stainless steel Carrera's, the 510.50x, the Silverstone, the Cortina, Audi Sport, AMI etc. A kind of in-house movement as it were, though not strictly speaking.
For a number of them, most likely including the 510.523, it looks like Lemania also may have provided at least some blueprint of the case design, as others that are very similar can be found in other brands, which would have been unlikely had this been a true proprietary Heuer design.
Cheers,
Fabrizio