in http://www.bjsonline.com/watches/articles/0018_1.shtml as referred to above it also states "The ref. 6536/1 also had a chronometer rated movenent, Cal 1030, 25 jewels, adjusted to temperature and 5 positions(without "-1" has a non-chronometer movement). The dial was a black gloss, gilt print, with deph in silver, and also note the case was not as thick as the Ref 6536 which it had replaced."
check http://www.rolexforums.com/showthread.php?t=30759 (might need to register to see it) where it says;
6536 - Launched in 1955. Upgrade of the 6205 model. Depth rated to 100m (330 ft) with the 8mm crown. No crown guard and no depth rating on dial. Submariner printed on dial. First time use of the Mercedes hands. Movement upgraded to the non-chronometer 1030 with 25 Jewels. Updated in 1956. Depth rated to 100m (330 ft) with a 8mm crown. No crown guard however depth rating now printed on dial (white). Submariner also printed on dial. Non-Chronometer 1030 movement. First time Bezel contained markers for first 15 minutes.
6536/1 - Launched in 1956. Depth rated to 100m (330 ft) with a 8mm crown. No crown guard with depth rating printed on dial (white). Model name also present on dial. Chronometer 1030 movement with 25 Jewels. Bezel with markers for first 15 minutes. Triangle on Bezel painted red.
Also note the 5508 different caseback here http://mob.watchprosite.com/show-forumpost.../ti-439421/s-0/
nice site by the way