Looks like this covers the "How To's" and "Which Computation method do I use" questions on arriving at the proper calculating of retirement, severance, and TDRL/PDRL pay calculations FOR USE BY FINANCE.
http://comptroller.defense.gov/fmr/current/07b/07b_03.pdf
DoD 7000.14-R
Financial Management Regulation Volume 7B, Chapter 3
*March 2013 - INCLUDES UPDATES
http://comptroller.defense.gov/fmr/current/07b/07b_03.pdf
V/r,
nwlivewire
http://comptroller.defense.gov/fmr/current/07b/07b_03.pdf
DoD 7000.14-R
Financial Management Regulation Volume 7B, Chapter 3
*March 2013 - INCLUDES UPDATES
http://comptroller.defense.gov/fmr/current/07b/07b_03.pdf
V/r,
nwlivewire