The correct term is present tense - we do not know. There could be new information in the future that changes our understanding. Of course, there's scope to speculate in the meantime...
I reckon it's a Powerpoint presentation for farmers, and later, an observation tool. Most of it is pictorial or representative rather than realistic: here be stars, here be ye sun, here be ye moon, from which ye may infer that our discourse be about ye celestial objects. The significant features from the point of view of transferring useful farming information are the two large arcs and the group of seven stars close together. For this to be viable, we need to accept the following...
The two arcs represent the range of places along the eastern and western horizons where the sun rises and sets throughout the year.
The group of seven stars close together represent the Pleiades star cluster.
If you happen to be a farmer at this sort of latitude, the visibility or not of the Pleiades can be a handy indicator of when to sow seeds and harvest crops - it's only visible over the winter period. Outside of that, it's more or less close to the sun and is thus obscured. The transitions between visible and obscured, and back again, are pretty close to suitable sowing and harvest times.
If we first imagine the disc without the arcs (which were added later), then it could serve as a visual aid as part of an explanation on when to sow and harvest... Blah, blah.. night sky... blah.. look for the group of seven stars during winter... blah... when you can't see them any more, it's time to sow... blah... after summer and you can see them again, it's time to harvest.
So where do the arcs come in? It's possible that they could be used to aid in the timing of sowing and harvesting. Let's say the disc was attached to a fixed object like the neatly-flattened top of a tree stump, perhaps nailed down. Every day, we hang about in the evening and wait for the sunset. When the sun sets, we make a couple of marks in the edge of the tree stump, on opposite sides, to act as sights towards the position of the sunset. After a year, we end up with series of marks spanning the eastern and western parts of the circumference of the stump. We might watch this for another year, or even several years, and eventually conclude that the sun only rises and sets somewhere within these arcs. We further note that, when the sun rise and set points are moving northwards along the horizons, the Pleiades become obscured at about mid-way.
The correlation between the movement of the rise and set points and the obscuration of the Pleiades means we can tell when the obscuration of the Pleiades is getting close, which gives us time to prepare for sowing. Likewise, when the rise and set points are moving southwards from mid summer, and approaching the mid-point, we can tell when the reappearance of the Pleiades is getting close and can prepare for harvest. For all the other times, when the rises and sets are well away from the east-west line, or close but moving away, we don't have to concern ourselves with sowing or harvesting and can get on with other things (like going down the local caves and painting Powerpoints for budding hunters).
If we consider this additional aspect of tracking the sun, giving us an element of planning, to be useful, we could mark the range of rise and set points on the disc with a couple of arcs. We could then incorporate a description of the sun's rise and set points, and how they can help with timing of sowing and harvesting, into our Powerpoint of How To Succeed As A Farmer. We could even drag our farming acolytes up to the disc at suitable times of year to demonstrate that the sun rises and sets in different directions and how the Pleiades appear and disappear when the sun is rising and setting somewhere along the east-west line between the mid-points of the two arcs.
Note that sun
set seems to me to be more useful than sunrise because you can look for the Pleiades in the night sky after the sun has gone down. If it was all about sunrise, you'd have to wait all day before you can look for the star cluster.
This is just speculation, but is based on the notion that astronomy had to come from somewhere, and that the regular motion of some celestial objects could well have been correlated with notable times of the year, like new plant growth in spring and maturity in autumn. Couple that with the idea that plants drop seeds to make new plants, then a hunter-gatherer might do 2+2 and develop the concept of planting seeds now to get edible mature plants later. If there's a celestial correlation with this, and if you've had a few bad growing seasons when there wasn't much food, you might want to look at the celestial motions in more detail and synchronise your planting and harvesting with particular celestial events.
