A calorimeter board is provided for power calibration of a laser emission. The board includes a flat metal plate, a sinuous groove and a resistance temperature detector wire. The flat metal plate has obverse and reverse surfaces separated by a thickness. The groove is cut into the reverse surface and penetrates to a depth being part of the thickness. The wire is disposed within the groove at the depth. The wire connects to an instrument that measures electrical resistance responsive to the laser emission on the obverse surface.