This may be a very accurate guesstimate for Galah's purposes but the accuracy is dependent on the film in use, the scene, the subject, the style, and the intent.
Example; I did an event at a ski resort, the start of a race course, a few weeks back the participant's faces were in open shade, the snow around them was in full sun, there was a dark evergreen forest behind them.
The faces of the people were in a low contrast setting, the rest of the scene is high contrast.
In a situation like this you have to decide what is most important to you and which method/tool for metering will work best.
A white card two stops up may have led me astray in that situation.
There is no substitute for experimenting for yourself.