It's obvious that Ken put his time in with a gear inch formula to actually get himself a front chainwheel/rear cassettes combination that would give him less overlap. This from the folks at "Bike at Work, Inc".
Gear Ratios and Gear Inches
The overall gear ratio of a bike, trike, or other type of human-powered vehicle (HPV) is determined by the size of the sprockets (gears) and the wheel diameter. The effective gear ratio of a particular sprocket combination on a bicycle is easily calculated using the following formula:
# of teeth on driving sprocket
------------------------------------- X wheel diameter
# of teeth on driven sprocket
If the wheel diameter is measured in inches, this formula produces a result in units of gear inches. Gear inches are often used to compare the gearing of different HPV's.