A scale intercomparison between a C-series calorimeter and a commercially available, virtually 100-percent quantum-efficient photodiode device has been undertaken." The intercomparison has been performed at the helium-neon laser wavelength (632.8 nm) with power levels incident on the photodiode device ranging from 4 JlW to 1.4 mW. Results obtained when the photodiode device was reverse biased with 9 and 18 V indicate that the scales of the photodiode device and the Cseries calorimeter are linearly related with an average correction factor of 1.0047 and 1.0037, respectively. 2 6 5 4 3 7