. "From sundials to atomic clocks : understanding time and frequency / by James Jespersen and Jane Fitz-Randolph ; illustrated by John Robb / [Washington : National Bureau of Standards, U.S. Dept. of Commerce] : for sale by the Supt. of Docs., U.S. Govt. Print. Off. , 1977" . . . . . "1977"^^ . . . "5"^^ .