These are memoranda which have been issued by USCIS (and INS prior to the creation of USCIS) on this topic. You will need the free Adobe Reader software to view these files.
Procedures for Calculating the Maximum Period of Stay for R-1 Nonimmigrants (AFM Update AD12-03) (70KB PDF)03/09/2012
Clarifying Guidance on the Implementation of the District Court's Order in Ruiz-Diaz v. United States, No. C07-1881RSL (W.D. Wash. June 11, 2009) (253KB PDF)Signed Donald Neufeld, Acting Associate Director, Domestic Operations, August 5, 200908/05/2009