On the one hand, an orrery is probably the existing invention that Almagest most closely resembles. On the other hand, the spirit in which Almagest is conceived is very different.
An orrery is a working model of the 'solar system'. The original orrery was built by George Graham and Thomas Tompion for Charles Boyle, the fourth Earl of Orrery, in 1712.
Not many years earlier (1687) Sir Isaac Newton had shown how the orbits of the heavenly bodies may be calculated in great detail using his three Laws of Motion together with the Inverse Square Law of gravity. The hypothesis of Copernicus and Galileo, that the sun stands still at the centre of the solar system, with the earth and other planets revolving around it, was apparently justified, since it was now part and parcel of an elaborate theory which could produce extraordinarily accurate predictions.
It was time for anyone who regarded themselves as 'modern' to finally purge themselves of what had for millennia been regarded as common sense: that the earth under our feet is what is standing still, while the sun and the starry sky turn about the earth. Of course this change of outlook had been 'in the air' for many decades, but during the 1700's it became virtually compulsory for any educated person.
The problem with the heliocentric point-of-view has always been that it defies common sense: it does not agree with what one actually sees. Orrery-building may be regarded as an attempt to help overcome this difficulty. An orrery demonstrates what one would see if one could view the solar system from outside - from outer space. What God sees, in fact.
Almagest represents a fusion of the two beliefs
It uses the Newtonian theory to calculate the positions of the planets, as viewed from earth, but then presents the results as if the geocentric theory were the true one.
Almagest could be described as a geocentric, digital orrery. But an orrery as traditionally conceived, it is not!
No. Almagest is wholly original in concept and design.
As explained above, it differs from an orrery in that it puts the earth at the centre of the cosmos. In earlier times, before the Scientific Revolution of the 17th and 18th centuries, astronomical clocks were built whose aim was essentially similar to Almagest's, that is, to show the movements of the sun, moon and planets as we actually observe them in our sky. The difference between those clocks, impressive as they are, and Almagest is that their workings were limited to clockwork machinery, whereas Almagest makes use of digital electronics to aid it in its task of reproducing the movements of the heavens. As a result it is more accurate, more versatile and infinitely easier to set up and use.
Almagest is an innovative product, produced in small quantities. Most of its 250-odd parts are specially made for it, to a high standard. We haven't skimped on the quality - or the quantity - of the materials. Most of the working parts are of brass, with the designs on the Zodiac Ring and the Horizon Plate etched into (not printed onto) the brass. The wooden base is oak. We have gone to great lengths to make the Control Box easy for anyone to use; and made it separate from the clock itself (communicating by means of infra-red beams), so as not to detract from the elegance of the main unit.
The dimensions of Almagest are 13" high by 15" diameter (330mm by 380mm). It weighs approximately 40 lbs (18 kg) - make sure you have a sturdy table to place it on.
Make sure you enter your latitude and longitude at the same time as you set the time of your Almagest.
Just one proviso: Almagest is designed primarily for use in the Northern Hemisphere. If you live in the Southern Hemisphere (more than say 15 or 20 degrees South of the equator), the relationship between Almagest's 'clock face' and what you see in the sky will not be quite so direct as if you lived in the Northern Hemisphere. For example, during the day, Almagest's sun moves from left to right across the clockface. Whereas, the actual sun (in the South) moves from right to left. During the course of a year, the sun moves through the signs of the Zodiac in the order Aries, Taurus, Gemini, etc... (this is the same for everyone). Looking at the corresponding constellations in the sky, Gemini is to the left of Taurus, which is to the left of Aries - in the Northern Hemisphere: the other way round in the South. Again, Almagest takes the Northern view (so Taurus is to the left of Aries).
Wherever you are Almagest will show the sun rising at the correct time, the moon likewise, will place the planets in the right signs, etc. If you live in the South, you will just have to think a bit harder to connect the 'clock face' with what you see in the sky (basically, they are mirror images of one another).