The 1533 Models are perhaps even rarer still than the 73633 and 1133G. These are driven by the calibre 15 movements and were also introduced in 1972. The 1533G (with denim blue sub register) changes between silver, grey and gold depending on the lighting conditions. The 1533B (with white or grey sub register) changes between a royal blue and a darker navy, but can almost look black in some lighting. The same issues apply to this model, seal, hands, dial, except it is even rarer to find one of these B or G variants with a clean mint dial, due to seal issues. Also note that the majority of these variants appear to come with a 1133 case, so if you find one that has a 1533 stamped case as Heuer often put 1533 models into 1133 cases (the 1133 and 1533 case sizes were identical).