We can use Fig. 8.9 on page 489 to approximate power calculations if we do not have an appropriate computer program handy. For instance, in Example 8.6.1 , if the Llanederyn mean is less than the Ashley Rails mean by … , then … The power of a level 0.01 test of … appears to about 0.65 in the right panel of Fig. 8.9. (The actual power is 0.63.)