If multiple analysts will read parts of the same slide, then all analysts need to read in the same fashion and direction.
Use the x and y coordinates on the microscope stage to determine if each row height or column width is equal every time an analyst moves and is equal between analysts.
When an organism must be examined at higher magnification, record the location and the direction of scanning so that you may return to the exact location before resuming scanning.
If counts from multiple analysts differ by >10%, check slide scanning technique for each analyst.