High School: Transcripts & Calculating GPA

Keeping accurate transcripts is an important job for me once my kids reach high school.  Colleges want to see not only what subjects we studied but their degree of difficulty.  That is when calculating GPA becomes complicated.  Colleges look at the weighted and unweighted GPAs to evaluate difficulty, and they also do their own GPA calculations.  So, honors classes, dual-enrollement, AP classes all weigh in differently from regular classes.  Each district has its own standards, and since we are registered as homeschoolers at our County School Board, I am using their standards for GPA calculation.  The Hillsborough County School Board says we can add .04 points for each honors .5 credit class.  Their policy for dual-enrollment goes like this:

Dual enrollment courses will receive the same course weighting as Advanced Placement courses. A bonus of .08 is added to the cumulative GPA for every one-half credit and .16 per 1.0 high school credit for each duel enrollment course in which the student earns a grade of C or higher. Since college credit is awarded, this grade will remain a part of the college transcript. Students are limited to nine (9) credit hours for fall, nine (9) credit hours for spring, and nine (9) credit hours for summer, not to exceed 27 credit hours per academic year.

Creating a weighted vs. unweighted GPA is important in producing a good transcript.  I base my GPA on the following letter-grade values:

A = 4.0
A- = 3.7
B+ = 3.3
B = 3.0
B- = 2.7
C+ = 2.3
C = 2.0
C- = 1.7
D+ = 1.3
D = 1.0
F = 0

So, if my son took seven classes, one of them being a PE class that only counted for a half credit (.5) and another one an honors class, he has 6.5 credits.  Say he got five As, and one A- in one of the regular one credit classes,  here is how I would calculate weighted and unweighted GPAs:
4 x 5.5 = 22 ,  22 + 3.7= 25.7 ,   25.7 / 6.5 = 3.93
Unweighter GPA = 3.9
3 x 4.5 = 13.5 ,   4.8 + 3.7 = 8.5 ,   13.5 + 8.5 = 32 ,   32 / 6.5 = 4.71
Weighted GPA = 4.71