Section 23.A.35 of the contract lays out the formula.

Hope you're good at math.

(actually its not that complex, just a lot of inputs if you have training, vacation, etc.)

“Reserve assignment weighting” (RAW) means a value assigned to a reserve pilot that is
based on his accumulated credit in a bid period and his CROC days in a bid period. A
reserve pilot’s RAW is used to sequence him for assignment to open time. Such value
will be calculated using the following formula, rounded to the nearest integer:
Reserve assignment weighting = [(A ÷ C) x 75] + [(B ÷ D) x 100], where:
A = the reserve pilot’s credit hours accumulated in the bid period plus prorated credit
hours associated with his period of unpaid absence and/or vacation and/or training
(other than qualification or distributed training), if any. The number of prorated
hours associated with his period of unpaid absence and/or vacation and/or training
(other than qualification or distributed training) will be determined by multiplying the
number of days of his unpaid absence and/or vacation and/or training (other than
qualification or distributed training) by the reserve guarantee and then dividing that
product by 30 or 31 (days of the bid period).
B = the reserve pilot’s CROC days plus prorated CROC days associated with his period
of absence other than sick leave, if any (e.g., vacation, training, MLOA, PLOA). The
number of prorated CROC days associated with his period of absence other than sick
leave will be determined by multiplying the number of days of his absence by 18 (oncall
days per bid period) and then dividing that product by 30 or 31 (days of the bid
period).
C = the reserve guarantee.
D = number of on-call days in a full month of reserve.

"CROC" day is a credited reserve on call day. (section 23.A.8)