IMHO the chapter ring is a design throwback, if you see what I mean. Given the period of time that the 5512 was designed the chapter ring is a nod to the past. The 5513's lack of chapter ring sets the tone for the future. Now don't get me wrong - I'm no modernist but I do tend towards simplicity of design with no added unnecessary flourishes and as such I prefer the 5513. As far as I'm aware there is no functional reason to have a chapter ring on the index. So if you like the 5513 is the 'purer' design, there is nothing on it that I can see has been put there for 'show' or aesthetic reasons, everything is functional even the wording. I also realise that there is no hard and fast rule, some 5512's had no chapter ring and some 5513's did (according to Urul & Skeet).