You can read about how PD/WPI ratings are done here...http://www.dir.ca.gov/dwc/PDR.pdf
The labor code also provides inforamtion/statute that governs PD/WPI ratings...
4660. (a) In determining the percentages of permanent disability,
account shall be taken of the nature of the physical injury or
disfigurement, the occupation of the injured employee, and his or her
age at the time of the injury, consideration being given to an
employee's diminished future earning capacity.
(b) (1) For purposes of this section, the "nature of the physical
injury or disfigurement" shall incorporate the descriptions and
measurements of physical impairments and the corresponding
percentages of impairments published in the American Medical
Association (AMA) Guides to the Evaluation of Permanent Impairment
(2) For purposes of this section, an employee's diminished future
earning capacity shall be a numeric formula based on empirical data
and findings that aggregate the average percentage of long-term loss
of income resulting from each type of injury for similarly situated
employees. The administrative director shall formulate the adjusted
rating schedule based on empirical data and findings from the
Evaluation of California's Permanent Disability Rating Schedule,
Interim Report (December 2003), prepared by the RAND Institute for
Civil Justice, and upon data from additional empirical studies.
(c) The administrative director shall amend the schedule for the
determination of the percentage of permanent disability in accordance
with this section at least once every five years. This schedule
shall be available for public inspection and, without formal
introduction in evidence, shall be prima facie evidence of the
percentage of permanent disability to be attributed to each injury
covered by the schedule.
(d) The schedule shall promote consistency, uniformity, and
objectivity. The schedule and any amendment thereto or revision
thereof shall apply prospectively and shall apply to and govern only
those permanent disabilities that result from compensable injuries
received or occurring on and after the effective date of the adoption
of the schedule, amendment or revision, as the fact may be. For
compensable claims arising before January 1, 2005, the schedule as
revised pursuant to changes made in legislation enacted during the
2003-04 Regular and Extraordinary Sessions shall apply to the
determination of permanent disabilities when there has been either no
comprehensive medical-legal report or no report by a treating
physician indicating the existence of permanent disability, or when
the employer is not required to provide the notice required by
Section 4061 to the injured worker.
(e) On or before January 1, 2005, the administrative director
shall adopt regulations to implement the changes made to this section
by the act that added this subdivision.
Once your PTP/AME calculates a PD rating that rating/number will be converted to a WPI rating and that will be the basis for your ''award'' for PD indemnity...
The 12% is worth 5 weeks for each 1% of the rating..or 60 weeks, payable at around $230/wk or $13,800 give or take 15% depending on the factors of your case.
Recent decisions on case review/appeal and actions taken by the legislature have resulted in some potential changes in the PDRS..while this may or may not affect your case, you can read this blog ...http://www.workerscompzone.com/ and see what's happening in the WC arena.