Wichamstow is just one of the more than 3,000 estates in Anglo-Saxon England with a watermill (many of these estates have more than one mill). Although the mill belongs to eorl Godwin, Leofmar ðe Mylenwyrd rents it, and grinds grain into flour for most of the farmers and villagers of the estate.
The watermill has advantages over the windmill (which seems to appear in Britain by the 1200's), as it is less reliant upon the weather. However the windmill was to become the preferred type later on, where the water supply was too erratic or too fast.
Acmylen itself is a typical small mill, with a simple horizontal side shot mill wheel. That is to say, the water from the mill pond runs down the mill-race via the sluice gate, striking the wheel on one side (which is in reality a thick shaft with blades all around its circumference at the base). The sluice gate regulates the volume of water that strikes the wheel, and has to be judged with some care to prevent the mill stones from spinning too fast and vibrating too much. Even on a normal day, the speed that the wheel turns and therefore the speed that the millstones rotate is quite violent enough. In times of very heavy rain, water has to be 'drained' from the pond so that there isn't a huge volume behind the gate, which can lead to other problems running the mill.
The mill stones for the mill are themselves much bigger in diameter than those used in the home (these are called Querns). They come in two main types; Rotary Querns which are two stones sat one upon the other, with the top stone riding on an axle that sits astride a small but important piece of wood called a 'Rynd'. By adjusting these elements, you can set the desired coarseness of your flour. The process is similar to the mill in that the top stone is rotated against the lower stone with a handle. The grain is placed into a hole in the centre of the top stone, and as it is ground, the flour runs out from the seam between the two stones.
The other style of Quern is the Saddle Quern, which is an ancient design, but one which was still to be seen occasionally. This type has a large flat stone as it's base, with a smaller one for the top stone. Here you simply place grain on the lower stone and grind the top stone to and fro along the lower. Grinding grain into flour for the making of bread etc; can take some time, and was a job that was shared by anyone in the family who had the strength to turn the stones. Which is why, if you could afford the luxury of sending it to the mill, you would have done so.
The millstones in all of these cases were made from a variety of locally obtained hard rock. Millstone Grit is the most famous of these and became the standard used up and down the country by the 1700's before the advent of the concrete ones that are used today.
A favourite import was Rhenish Lava from northern Germany which is a type of Basalt, and is often associated with Viking sites. In all cases, the stones had to be shaped, balanced and dressed. The dressing was at this time a rough set of regular marks (chips) cut at right-angles into the grinding faces of the stones, to assist with the grinding. Old or broken millstones often found their way into houses as door-steps and footings.
On some estates, larger, more powerful mills with as many as three linked vertical overshot wheels were used. These were more powerful than other types of mill wheel, as gravity assists in turning the wheel, which means you can be more economical with the water stored in the pond.