Figure 2.

Second step of the interchangeability method to assess changes in measurements between 2 methods of measurement. Initial point A changes to point C, which is situated inside the zone between the 2 interchangeability lines (dotted red lines, defined as [(X = Y(1+R)+(1+R) (RM₁−TM₁)) and (X = Y(1−R)+(1+R) (RM₁−TM₁)]), D if only the repeatability overlaps with the same zone, or E if neither the point itself nor its repeatability interval overlap with the same zone. R = repeatability, RM₁ = first value measured with the reference method, TM₁ = first value measured with the test method.