Another technique involves simply timing the altitude gained  over 30 seconds or 1 minute. Theoretically, the optimum average speed is attained if the  MacCready ring is set for the achieved rate of climb within  the height band. To do this, rotate the ring so that the index  mark is at the achieved rate of climb (for instance, 400 fpm)  rather than at zero (the setting used for maximum distance).  A series of climbs and glides gives the optimum balance  between spending time climbing and gliding. The logic is  that, on stronger days, the extra altitude lost by flying faster  between thermals is more than made up in the strong lift  during climbs. Flying slower than the MacCready setting  does not make the best use of available climbs. Flying faster  than the MacCready setting uses too much altitude between  thermals; it then takes more than the optimum amount of  time to regain the altitude. Strict use of the MacCready ring assumes that the next  thermal is at least as strong as that set on the ring and can be  reached with the available altitude. Efforts to fly faster must  be tempered with judgment when conditions are not ideal.  Factors that may require departure from the MacCready ring  theory include terrain (extra height needed ahead to clear a  ridge), distance to the next landable spot, or deteriorating  soaring conditions ahead. If the next thermal appears to be  out of reach before dropping below the height band, either  climb higher, glide more slowly, or both. To illustrate the use of speed-to-fly theory, assume there are  four gliders at the same height. Ahead are three weak cumulus  clouds, each produced by 200-fpm thermals, then a larger  cumulus with 600 fpm thermals under it, as in  Figure 11-13. By the time pilot 4 has climbed under the large cumulus,  the pilot is well ahead of the other two pilots and is relaying  retrieve instructions for pilot 1. This example illustrates  the science and art of faster cross-country soaring. The  science is provided by speed-to-fly theory, while the art  involves interpreting and modifying the theory for the actual  conditions. Knowledge of speed-to-fly theory is important as  a foundation. How to apply the art of cross-country soaring  stems from practice and experience. The height band changes during the day. On a typical soaring  day, thermal height and strength often increases rapidly  •  Pilot 1 sets the ring to 6 knots for the anticipated strong  climb under the large cumulus, but the aggressive  approach has the glider on the ground before reaching  the cloud. •  Pilot 2 sets the ring for 2 knots and climbs under each  cloud until resetting the ring to 6 knots after climbing  under the third weak cumulus, in accordance with  strict speed-to-fly theory. •  Pilot 3 is conservative and sets the ring to zero for the  maximum glide. •  Pilot 4 calculates the altitude needed to glide to the  large cumulus using an intermediate setting of 3 knots,  and finds the glider can glide to the cloud and still be  within the height band. 1 3 4 2 Figure 11-13.  Example of glides achieved for different MacCready ring settings. Tips and Techniques 11-12