I have a copy of the CDCR 1897-U Calculation Worksheet. After discussing it in great detail with a few case analysts up north, I scanned it and recreated it in Excel...formulas and all. You can download both the scanned original in pdf format and the recreated Excel version in the zip file below. The Excel version has all the formulas and 4 spreadsheets for the various credit earning abilities (straight half, third + half, 80%, and 85%).
All you need to do is input the information requested in the pink highlighted cells (Term Imposed, Pre-sentence Credits Awarded by Judge at Sentencing, Date of Transfer to State, and Sentencing Date) and everything will auto-populate and calculate.
I recreated the section on the right (Section B) to be specifically formulated to re-calculate EPRD once 1/3 time for camp/institution firefighter or assignment to camp has begun. Time should begin once training is completed per SBx3 18 (prior to that it was only after transfer to assigned camp that the inmates were eligible for 1/3 time), although I can't confirm that that's how they are doing it.
Anyway, the info currently in the "Third + Half" spreadsheet and the "80%" spreadsheet is my husband's current term and prior term, respectively, and both equate to the exact dates given by the CDCR so I'm fairly certain of its accuracy although I make no guarantees. You can compare my husband's prior term (80% spreadsheet) to that in the scanned original.
Feel free to let me know if you have any questions!