Originally Posted by Roger Cole
The difference between 5 versus 4 or 6 seconds is only 20%. Insignificant especially with color neg. Always err on the side of more exposure with color nef so give it 6 and don't worry about it.
It's for HP5+.
And it is more than 20%, as you have reciprocity failure on reciprocity failure.
But my point was, it is not an accurate graph, particularly for shorter exposures.