On any long voyage, ocean or coastal, or even a long inland sail, it is generally crucial that the helmsman has in mind the proper or desired course at all times. This is especially true on overnight sails and any time in bad conditions. Generally in big waves and strong winds it is important to know the right course that keeps you in tune with the sail trim, wind, and seas.
On a long trip, when the course is changing frequently, it is easy to lose track of the course. For example, if you steered 220 all day yesterday, but now this morning the right course is 245, then if you are thrown off course by a wave, you might instinctively turn back and try to settle in at 220, which would be wrong. The delay in doing this right could be crucial in very tough conditions.
Besides safety, there is efficiency. With changing crew, you might forget to tell the new watch that the course changed, etc... and off you go for some period of time on the wrong course.
The solution to this is to have some prominent place in clear view of the helmsman that shows the present proper course. Whenever the navigator comes up with a new course, it is marked in that sign, and all know it. You could rig any device for this. At times we have used a vertical piece of duct tape, and then just crossed off the old course and wrote in the new one below it. That has the virtue of keeping a record of your courses if doubt comes up. You could also just write it on the bulkhead with some type of erasable marker after testing that it does not stain your fiberglass (most do!) Or better, use a small dedicated board for this purpose.
In the old days of sailing, they used a course box. I found this antique one for sale on ebay in Sept, 2009. This one is about 10 inches across. You lift the pins to rotate to a new digit. Nice idea, and modern equivalents are easy to imagine. The existence of these show clearly that this was an issue faced by sailors since earliest times.
Note: in earlier writings we have referred to this as a "route box," but it seems course box is a better term. I do not know what the official name was or is. As we run across this in our work we are changing all to course box.