Radiometer two-point calibration

For a stable linear radiometer, known cold and hot radiances give $B_S=B_C+(B_H-B_C)(V_S-V_C)/(V_H-V_C)$. Put $a=(B_H-B_C)/(V_H-V_C)$ and $b=-a(V_S-V_C)/(V_H-V_C)$. Then $\delta B_S=a\delta V_S+b\delta V_H-(a+b)\delta V_C$; all three measured voltages contribute to the retrieved uncertainty.