Hi Tom,
some time ago you mentioned the poor accuracy of the ceramic resonator as time base of the Arduino Atmega2560 board to be more than 1000ppm. Would it be possible to calibrate the board by using a RTC device, e. g. the DS3231 from Maxim? I think this would help all DIY builders among us who are missing the excellent stability of 10ppm of your original AstroEQ board!?
Andreas