Chemists also count atoms when naming a sigmatropic shift where a hydrogen atom moves. The carbon chain does not break in a hydrogen atom migration. So, chemists count across all atoms involved in the reaction rather than only across the closest atoms. For example, the following hydrogen atom migration is of order [1,5], attained by counting counterclockwise through the π system, rather than the [1,3] order through the ring CH group that would mistakenly result if counted clockwise.