The cover of The Designer's Guide to High-Purity Oscillators continues the map theme of The Designer's Guide Series. In this case, the map is a nautical chart of the entrance to San Francisco Bay. Superimposed is a picture of the Harrison H4 clock. These are appropriate as high-purity oscillators play a critical role in accurate timekeeping, and as a result, the long range navigation of the seas. The H4 clock was the first clock that was good enough to provide accurate dertermination of longitude after a long journey, such as a crossing of the Atlantic Ocean.

Read the facinating story of the Harrison H4 clock in The Harrison-Maskelyne Affair in the September/October 2003 issue of AmericanScientist Online. And you can find more about the importance of Harrison's chonometer in The Science of Timekeeping by David Allan.