Final answer:
The rule of thumb for reading a point designation grid is to stop at the first point of difference, even if the order may change later. You need to identify the central point and determine the ranges around it. Stop at the first point that differs from the central point and note that as the range.
Step-by-step explanation:
The rule of thumb for reading a point designation grid is to stop at the first point of difference. This means that you should identify the central point and then determine the range of points around it.
Once you reach the first point that differs from the central point, you should stop and note that as the range.
For example, if the central point is 1 and the range is 0.5-1.5, then the first point of difference would be 1.5.
If the central point is 2 and the ranges are 1.5-2.5, 2.5-3.5, 3.5-4.5, and 4.5-5.5, then the first points of difference would be 2.5, 3.5, 4.5, and 5.5 respectively.
Remember to follow these rules even if the order may change later, as indicated by the caution mentioned in the reference. Always stop at the first point of difference, even if the order changes later.