"This chart is a guide to determine the APPROXIMATE CAPACITY of all popular brands for each cavity. Actual charges may vary due to manufacturing tolerances of the cavities, powder and method of use. These charges are not safe to use for maximum loads without first checking them on a scale. Most of these loads are unusable for many cartridges. However, by not eliminating them at an arbitrary point, no mistaken inference of usable range could be concluded."
The above is copied from the very top of the powder chart that comes with each Pro Auto Disk.
Below is from the RCBS Uniflow instructions:
A dependable powder scale should be used to set the first charges in the powder measure as follows: throw a powder charge directly into the scale pan by raising the bandle and lowering it. Weigh the charge. If it is too heavy, adjust the measuring screw with the handle in the down position to a lower number. If the charge is too light, adjust the measuring screw to a larger number. When you arrive at the exact charge you need note the reading on the measuring screw and you're ready to throw a series of charges. Write down measuring screw setting for the powder and weight being used and you can quickly reset the powder measure the next time this charge is required.
Lee gives you a place to start, RCBS doesn't.
Several years ago I had (still do) an Ohaus Duo-Measure, very expensive and well built measure. The setting instructions for it was a graph.
NO measure gives you the exact settings for each load of the hundreds of powders available.
The all expect you to be able to read and follow instructions.
Education teaches you the rules, experience teaches you the exceptions (Plagiarized from Claude Clay)