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thank you for responding.  i use hebcal because it's reliable.  shabbos this past Friday was 6:28 in Ambler, PA.  hebcal showed the yahrzeit of yud zayen tishri beginning at 7:37.  that's what i don't understand - even if i add 18minutes to 6:28 it comes to 6:46.  if you have a chance, please let me know how 7:37 was derived.  thanks again and a gut moed -