Assalamu Alaykum wa-Rahmatullahi wa-Barakatuh.
With reference to the next ICOP Conference in Turky, it was mentioned the tri-zonal calendar suggested by Dr Mohammad Ilyas (Malaysia) should be considered (or even the bi-zonal one).
I have requested Dr Monzur Ahmed to send my his DOS program website and after a lot of searches, he has found most of the files. It is now hosted on our ICOUK website for your information.
Moon Calculator 6 by Dr Monzur Ahmed
From the tri-zonal calendar image below, you can see that the Eastern Zone starts from Pakistan/India eastwards. The Central Zone is Europe, Africa and Middle East. The Western Zone is the Americas.
For example, next Eids (Shawwal/Dhul Hijjah), all three zones give the same date so the whole world should have a united Eid on one day. This can only be possible if Saudi Arabia starts the month correctly with actual moon sighting, which may differ from the Ummul Qura calendar, as was the case this Dhul Hijjah 1436 AH.
Hence, I suggest the Turkish and Ummul Qura calendar criteria should be changed to
HMNAO/Yallop (A+B) then we will likely see Eid on one-day in most years throughout the world, InshaAllah.
PS.
For more more details on the science/fiqh analysis,
the old Hilal Sighting & Islamic Dates by Dr Salman Shaikh is still valid!
Wassalam,
Qamar Uddin, York (UK)