Quote Originally Posted by nicholai View Post
I assume it's the other way around; CHS100 is to be exposed at EI 200 in daylight.
That's right, in fact for a number of years a UK chain of photo stores sold EFKE films under their own brand name and they were sold as 50, 100 & 200 ISO films. So CHS 100 was Jessops 200.

I began using KB14 later renamed EFKE (Adox) 25 back in the 70's and in more recent years have used the Pl25 sheet film version, I expose & process at 50 EI, which is what I rate Tmax 100 at, and I process both for the same development times - sometimes in the same tank.