A double shot is a situation where a blot can be hit from two different attacking points. Counting the number of rolls (out of 36) that hit in a double shot situation is useful both for evaluating checker plays (e.g., choosing the play that minimizes opponent's shots, or evaluating a tradeoff between shots and some other benefit) and cube decisions (e.g., evaluating market losers or game-winning chances).
This page builds on the material in Shot Counting: Single Shots and assumes that you have memorized the number of rolls (out of 36) that hit a blot 1-12 pips away: 11, 12, 14, 15, 15, 17, 6, 6, 5, 3, 2, 3.
The simplest way to count double shots is to add the number of single shots from each attacking point, then subtract rolls that were double-counted. For example, for a double shot from 5 and 6 pips away:
More generally:
Total shots = (rolls that hit from first point) + (rolls that hit from second point) − (double-counted rolls that hit from either point)