I have just tried the method in NJ where, unlike in my home state of NC, shoulders are generous, so I was able to take measurements in both directions. A 300-m course at 49 deg with a tire pressure of 620 kPa gave a calibration factor of 479.157 rev/km (no SCPF). A few minutes later at 54 deg and 630 kPa I got readings over the 25-m course of 31.1, 31.0, 31.0 and 30.9 spoke intervals. Number of spokes were 32 and whole revolutions were 11. Calibration factor was 478.750 rev/km and after adjustment to 620 kPa (plus 0.133 rev/km for negative 10 kPa) was 478.883 rev/km. The % difference from that of the 300-m course was minus 0.057.
The result on the 25-m course was almost identical to the one I got 3 weeks earlier on 3/14/08 in NC. At 63 degrees and a pressure of 620 kPa, calibration factor without the SCPF was 478.906 rev/km. Again this differed from that from a 300-m course by minus 0.06 %.
Note that no meter is required for calibration using the new method, and once the number of whole revolutions have been manually counted, there is never the need to do so again.