You can "measure" ceo relatively by using a series of glazes with coe's that range from low to high. Glaze test tiles made from a clay body in each glaze and fire. The results will be a relative measurement of that bodies coe based on the calculated coe for the glaze series.
For example if clay "A" is glazed with 5 glazes (glaze 1~5) and it crazes on 1~4 you'll know that the clay has about the same coe as glaze #5.
This testing method is further described in "Mastering Cone Six Glazes." An excellent book that I recommend for anyone interested in glazes.