A student working on a cite-check asked us to decipher the abbreviations that appear after different versions of a piece of federal legislation in THOMAS search results.  (For those of you wondering what THOMAS is, it’s a Library of Congress website that compiles a wide variety of federal legislative information, including legislation, House and Senate committee reports, the Congressional Record, and more -- most of it is available in PDF format from the Government Printing Office.)  For example, if you search for H.R. 2520 on THOMAS in the records of the current session of Congress, you will see search results that look like this:

1.  Stem Cell Therapeutic and Research Act of 2005 (Received in Senate from House) H.R. 2520.RDS

2.  Stem Cell Therapeutic and Research Act of 2005 (Placed on Calendar in Senate) H.R. 2520.PCS

The letters that are tacked on to the end of the bill number (RDS and PCS) simply represent the different versions of the bill.  According to the Library of Congress, the meaning of these extensions "is largely explained in the preceding parentheses."  Thus, "PCS" stands for "placed on calendar in Senate," and "RDS" stands for "received in Senate from House."  Thanks to THOMAS for taking the time to create a useful and informative "Help" page!