In the mid 1800s the Bessel ellipsoid of 1841 or the Clarke ellipsoid of 1866 were widely used; the Hayford ellipsoid of 1910 may later have been used by the United States Coast and Geodetic Survey. The standard ellipsoid for western states in 1849—which is generally congruent with that year's version of the Astronomical Almanac—is implicit in California's constitutional boundary definition; incessant invention of new datums by new and potentially interested parties do not re-render the old boundary definition. Holding assumptions of the earth back-in-time, modern satellite assisted survey techniques can determine location and transform them onto old ellipsoids to within a centimeter.