Difference between the observed J magnitude and the model J magnitude computed from the derived mass and T_eff, as a function of T_eff. The vertical line marks the location of L0 dwarfs. The dotted line (at –0.753 mag) represents the offset due to the possible presence of unresolved binaries, the dashed-dotted lines represent the error in the magnitude determination, and the long-dashed lines represent the uncertainties in the age and distance of Praesepe. The horizontal solid line just traces zero.