"Readings for this method are normally made; using a flat face incident meter by duplexing, measuring pointed directly at the main source and measuring pointing toward the subject then finding the logarithmic average, or by using a single hemispherical incident meter reading."

Mark, could you expand on the technique? I think you are saying a flat face measurement of the source illumination is logarithmically averaged with a flat face measurement with the flat face pointed at the subject,
a single hemispherical domed measurement with the dome pointed at the subject (opposite of the typical incident measurement with the dome pointed back at the camera). Do I understand you correctly?