An Astrolabe used to treat the Humours
The astrolabe above can be used find the location of the stars above the person in question at his/her place and time of birth. This tool became useful to doctors attempting to treat or balance a patients emotional instabilities. By reading the stars (zodiac) that blanketed the sky at the time and place of their birth the medical doctor could prescribe counter measures to balance out the temperaments of the four Humours that people are influenced by.
How to use the Astrolabe
Use the back of the astrolabe to find the date in question in the calendar. Move the label round until it lines up with this date. Then read along the line of the label to see the position in the Zodiac calendar. On the front of the Astrolabe, line up the rule with the Zodiac unit found on the rete. Holding both rule at rete (fixed together), rotate the rete until the rule reaches the time of birth of the patient.
Having followed these instructions, all the stars that fall within the horizon line should be the project of stars at the time of the patients birth. Provide Prescription accordingly.