My timing methodology was to measure over six most important positions and three phases of wind (full, after 24 hours, and after 55 hours). This provides us 18 measurements for accuracy throughout the six positions and at three phases of wind, which looks like a good (if transient) gauge. For the SPB453 (the black dial), the six-way common for the three phases was -5 s/d (full wind), -12 s/d (much less 24 hours), and -15.8 s/d (much less 55 hours). For the blue dial SPB451, I bought -4 s/d, -6 s/d, and -11.8.
