Clearlab's fitting guide prefers a trial lens, taking the steeper base curve first, and gives three stock designs by average K: 41.25 and lower, 8.9 mm / 14.5 mm; 41.50 to 45.50, 8.6 mm / 14.5 mm; 41.75 and higher, 8.3 mm / 14.5 mm, which is not available in plus powers.
