To measure the reactor relevance of existing and planned confinement devices, we propose Bta5/4 and Pheata3/4 as dimensionless engineering parameters. These quantities - together with a density parameter that can be written as na3/4/Bt - have to be conserved in plasma physics identity experiments on different-size devices to respect the so-called Kadomtsev similarity constraints. They offer also a coordinate system to map the approach to the reactor regime. Theoretical and semiempirical models can be used in this coordinate space to produce isocontours for different dimensionless physics quantities, like the usual parameters *, *, and , but also for the intensity of collisional coupling, the excess of heating power over the L-H transition threshold, and the ratio of current redistribution to energy confinement time to visualize the distance to the regime of a fusion reactor.