5 C.F.R. § 591.209 – What is a price index?

(a) The price index is the COLA area price divided by the DC area price and multiplied by 100.
(b) Example:
COLA Area Average Price for Item A = $1.233
DC Area Average Price for Item A = $1.164
Computation:
$1.233/$1.164 = 1.0592783
1.0592783 × 100 = 105.92783.
(c) In the case of the final index, OPM rounds the index to two decimal places.