Values for the absorption edge energies were obtained using two different procedures: 1) direct x-ray absorption measurements which remove an electron from the inner-shell of interest to infinity and 2) combinations of transition energies between inner and outer shells and the electron binding energies of the outer shells.
The set of direct absorption measurements includes some entries obtained with crystals of known lattice spacing [13,14,15] and re-scaled absorption edge values from the Bearden database  and other sources . The numerical values for these directly measured edges are given in the "Experimental Energy - Direct" column. Except for the rare gases all of these entries are for solid targets. The numbers in the reference column with the subscript "d" are for the direct absorption measurements.
The combination procedure uses electron binding energies for the L, M, and N shells found in references [82-87] and inner shell transition energies available in this database. For most edges and elements, there are several combinations of transitions and binding energies (alternate routes) that produce values for the edge location. Numerical values and uncertainties can be obtained as the average and 1 standard deviation spread of these alternate routes, respectively, and are given in the "Experimental Energy - Combined" column. The table does not contain references for the edges obtained by the combination procedure.
There are a few edge measurements using the vapor phase of elements with Z in the 20 to 29 and 62 to 70 ranges [17-22]. Because these measurements closely approximate free atoms and the theoretical calculations assume free atoms, we include these measurements in the table. The numerical values for the vapor measurements are in the "Experimental Energy - Vapor" column. The numbers in the reference column with the subscript "v" are for the vapor edge measurements.