Selenium cells are active on both meters. Compared with my Master V that has just come back from Quality Light Metric. Readings taken today with an overcast sky. Master III reads ~1/2-3/4 stop over expose. Master IV reads ~ 1+ stop over expose. The III is a very nice meter. The IV has the easiest to read dial. The IV has lines on the dial, scribed in red, by previous owner. They should show in the photos. Both come with a leather case. III is $30 IV is $20 Price includes shipping.