Not too far back a reader asked for a demonstration of calculating primary directions by hand. It would be far to wearisome, and very boring reading to demonstrate all of the calculations, all at once. Instead I will only give them piecemeal, enough for anyone to gain confidence in trying the calculations themselves and with a bit more explanation as to what is being done. If you do have problems there is always the comments section to express what the problem is.
We will be concentrating our attention first on the MC and in the next article on the Moon. As both of these belong to the ‘big five’ Significators of directions, the other three being Sun, Ascendant and Part of Fortune.
Now the MC is probably the simplest Significator as only right ascension is considered when directing to it. And it is very easy to discover the RA (right ascension) of the MC or any other position with respect to the MC. If you look into your Tables of Houses, here those published by the Otto Wilhelm Barth Verlag, publishers of the Deutsche Ephemeride:

Tables of Houses caption
You will find at the top of each page the sidereal time, the longitude of the MC and its right ascension or RAMC. It is simply a matter of interpolation to calculate the exact degree of the RAMC. Our sample chart has 25 Sagittarius 07 on the MC. So we take the difference between 25 Sag 07 and 24 Sag 30 (0 deg 38) multiply by 60 (the difference in minutes between RAMC 265 and RAMC 264) and divide by the difference between 25 Sag 25 and 24 Sag 30 (0 deg 55). This gives us 0 deg 41 which we add to the earlier RAMC. So the RAMC of 25 Sag 07 is 264 deg 41.
If you refer to Wm. Lilly’s Christian Astrology you will see that he made a speculum (table) of the position of all major planetary aspects, antiscia and term positions. It is a very good idea. So for our example chart we have the antiscion of Jupiter at 28 Capricorn 31 and the sextile of Mercury at 2 Aquarius 12, to take two examples. Using the above method the RA position with respect to the MC would be 300 deg 38 and 304 deg 28 respectively. If we were to direct them to the MC the difference in arc would be:
antiscion Jupiter at 28 Cap 31, RA = 300 deg 38 – RAMC 264 deg 41 = 35 deg 57
sextile Mercury at 2 Sag 12, RA = 304 deg 28– RAMC 264 deg 41 = 39 deg 47
If we use the Ptolomaic Key of 1 deg = 1 year then the first direction would occur at the age of 36 (in 1995) and the second at roughly 40 years (1999)
According to Wm. Lilly the direction of Jupiter (either in body or by antiscion) gives “everyone preferment according to capacity” and the sextile of Mercury advances the native “in the study of Learning…” As you note the emphasis is always on 10th house affairs. So Jupiter will be beneficial and help expand one’s professional affairs, according to capacity. So a crown prince might find himself king and someone in higher management might find themselves head of the board of directors. Someone unemployed might finally be given employment. The same with Mercury. The sextile encourages learning in respect to profession. So the crown prince might find himself motivated to study the laws of the land more closely. The head of the board to learn the language of his major foreign customer and the newly employed person the chance to qualify themselves by going to evening school. Then of course the condition of the chart must be accounted for. What are Jupiter and Mercury Lords of? What is their celestial state in the radix? Are they dignified and well placed or the opposite? All of these factors modify the general statement. So Jupiter in bad celestial state might offer the opportunity but it might not be strong enough to give the crown prince the crown, he might just add another order to his collection of honours or the manager becomes vice chairman instead of chairman of the board or the newly employed person gets the secondbest job on his list.