I'll use your example and clarify a bit. First, you need to know the price of the favorite on your Pinny closer. Since Pinny MLB lines are 8 cents at +115, the closer should have been -123/+115. Next, you have to calculate the no-vig probability of the Pinny closer. There are two steps to this.
First calculate the no-vig implied probabilities of the Pinny closer. To do this, you can use these formulas:
Code:
Favorite zero-vig implied probability
= P(f) = -F/(100-F)
Dog zero-vig implied probability
= P(d) = 100/(100+D)
This yields:
P(f) = -(-123)/[100-(-123)] = 123/223 ≈ 0.55156950672645739910313901345291
P(d) = 100/(100+115) = 100/215 ≈ 0.46511627906976744186046511627907
Next, you calculate the lineset probability. Since we want the dog probability, we use the bottom formula of the two choices below.
Code:
Line set favorite probability
P(f)
= -----------
P(f)+P(d)
Line set dog probability
P(d)
= -----------
P(f)+P(d)
The lineset probability is then: 0.46511627906976744186046511627907/(0.55156950672645739910313901345291 + 0.46511627906976744186046511627907) ≈ 0.45748281875064109139398912708996
Rounding, we get a zero-vig probability of 45.7483% for San Diego, according to the Pinny closer.
From there, you can calculate your edge by multiplying the zero-vig probability (in decimal form) of the closer by the payout multiplier of your wager and subtracting from 1. The payout is the total amount returned if the wager were to win. This includes your initial wager. Since (at +130) you would receive your initial wager plus 1.3 times your wager, your payout multiplier would be 2.3. So your edge on this wager would be:
(.457483 * 2.3) - 1 ≈ 5.22%