I think I folow Tails77.
The key point to remember is that the 90/180 rule is a 'rolling' requirement, in other words, in any 180 days, the maximum time you can have spent in Turkey is 90 days. The fact that your time in Turkey may span 2 visas is irrelevant. It is not a simplistic calculation, but the way I satisfied myself that my desired time in Turkey was going to work, was by using a high lighter pen on a year to view calendar!