Quote Originally Posted by Stephen Benskin View Post
When adhering to the ISO standard's contrast parameters.
Right.

My emphasis was on the word "approximate" - because for a while in this thread I was trying to get my head around a mistaken concept. I was thinking that ΔX was giving us exact 0.3 Gradient.

It's OK for me that it's approximate.

Some things are exact. Like the 0.1 density.
Some figures are rounded. Like ΔX being 0.296.
Some things are given tolerance. Like 0.8 density +/- 0.05 in the ISO parameters.
And some things move around quite a bit. Like the endpoints which you choose to measure CI.