Back when that camera was new, mercury wasn't heavily regulated. One of my friends remembers playing with little pools of mercury in his elementary school science class but now many items long thought to be safe are known to be dangerous and lead is another heavy metal that has joined that list causing a lot of obsolescence and other problems in the electronics component industry.
As others noted, you can always use a light meter. I hadn't owned or used one in years but two years ago I bought a Hensel studio strobe setup and a light meter to go with it. A separate light meter is a near necessity for properly setting up a group of studio strobes and is a handy tool to own. I went with an inexpensive Gossen "Sixtomat F2" rather than the same meter rebranded by Hensel which was over twice as much with the only addition being a button on the meter to test trigger the strobes. I use the Hensel app on my iPad for setup/adjustment so I didn't need a $200 button 🙂
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
