PPT Slide
VCT Literature References
"Collection and analysis of powder diffraction data with near-constant counting statistics", I. C. Madsen and R. J. Hill, J. Appl. Cryst. (1994). 27, 385-392 http://www.iucr.org/cgi-bin/paper?hz0014
Philips Friendly Fortran source code that does this Hill and Madsen method is at:
http://www.ccp14.ac.uk/ccp/ccp14/ftp-mirror/csirominerals-anon-ftp/pub/xtallography/variable-count-time/
(Original Hill and Madsen VCT (variable count time) Paper), I. C. Madsen and R. J. Hill, Adv. X-ray Anal. (1992), 35, 39-47
W. I. F. David, Accuracy in Powder Diffraction, Abstract P2.6 NIST Special Publication No. 846, Page 210, (1992) National Institute of Standards and Technology, Gaithersburg, MD, USA.