In cases where multiple types are available, more recent classifications were generally preferred, with some account being taken of reliability if this was possible. In such cases, the principal spectral types are followed by the TiO types given in parentheses, or their presence is indicated in the remarks. This code allows for simplified sorting according to variable-star designation, ordinarily a difficult procedure because of the nonstandard sequence used for name assignments. There are 334 letter designations followed by numerical codes corresponding to V 335, V 336, etc. Annual precession, given in arc minutes.
Units are Julian days.
For well-studied Miras and some semiregulars having reasonably constant periodicities, mean values of the periods for the entire observed intervals are usually reported, since they may be considered the most probable values for predicting future epochs. For U Gem and recurrent novae, the mean cycle values are given if known. These are denoted as differing from the periods of regular and semiregular variables by the presence of parentheses around the value. The values, in many cases, have been derived by the catalog compilers on the basis of all reliable independent determinations, with an indication of their approximate accuracy contained in the reported values. Photoelectric values were strongly preferred.