~1s per day is normal for a non-temperature-compensated quartz crystal. The cheap solution is to just sync to LF time transmissions (or GPS if not running on battery power).
The F-91W might not actually have anything resembling software; just fixed function mixed-signal circuitry, but I haven't investigated it. Given the timing of its release, it's possible that an HDL was used, but also possible it was designed at the circuit level with CAD. The F-87W (which the 91W replaced) predates either VHDL or Verilog.
The F-91W might not actually have anything resembling software; just fixed function mixed-signal circuitry, but I haven't investigated it. Given the timing of its release, it's possible that an HDL was used, but also possible it was designed at the circuit level with CAD. The F-87W (which the 91W replaced) predates either VHDL or Verilog.