If you work with older cameras with selenium light meters, you may find it useful to get a shoe mount digital light meter such as the Reflx lab light meter from Ali or Temu. The instructions may be in Chinese, or in such fine print that its is hard to read. Here is some help:

• Power On/Off: Press the middle button ("y") to turn it on. To turn it off, hold the left button ("a") for 3 seconds. It also features a 5-minute auto-sleep mode.
• Metering: Press the middle button once to wake the device or lock a reading.

• ISO: Hold the right button ("ß") for 3 seconds until the ISO icon flashes. Use the left/right buttons to adjust (range: 8–6400) and press the middle button to save.
• Switch Mode (A/T): Double-click the middle button to toggle between A (Aperture Priority) and T (Shutter Priority).
  • A-mode: You set the aperture; the meter calculates the shutter speed.
  • T-mode: You set the shutter speed; the meter calculates the aperture.
• Exposure Compensation (EV): Hold the middle button for 2 seconds until "EV" appears. Use the arrows to adjust by up to +/- 2 stops.