There are two types of “housing” systems used in Astrology.
So you can use either technique to determine how you are going to calculate your Midheaven and Imum Coeli.
The first is using all the houses by counting around by Ascendant. Ascendant = 1st House ruling sign.
If Ascendant = Aries, then Imum Coeli would be Cancer and Midheaven would be Capricorn. If Ascendant = Taurus, then Imum Coeli would be Leo and Midheaven would be Aquarius, etc etc.
The second system does not use whole house systems.
Calculating each house by specific degrees.
Such as the Ascendant starts at 26 degrees, so because not all the signs are the same size, then where the 26 degrees intersects is sometimes not the actual 4th sign but maybe the 3rd or 5th or etc.
Both of these methods are correct for different things.
Such as, say in a reality perspective. According to the government, your house ends at your fence line.
But according to your neighbour’s tree which grows over the fence and hangings over your backyard, it grows as it wants regardless.
So from the trees aspect the house lines are according to its growth, according to the government the lines are fixed.
Both systems are necessary for a) trees to be trees and exist, b) constrictions as saturn to exist in the world.
So both systems work, within different contexts.
So, in terms of whole house aspects, as an example, you can use whole houses for calculating the imum coeli, but use specific house degrees for planets.
Or vice versa, or whatever other variant your including. It just depends on how your looking at it.
So, for an example.
Say an Ascendant in Aries is at 26 degrees Aries.
This makes Aries/Mars the ruler of the 1st House, even though its 26 degrees into it.
A whole house system would make: 1-30 degrees of Aries the totality of the 1st house.
A degree house system would make 26 degrees Aries to approx 26 degrees Taurus the 1st House.
What I find is that most systems use the whole house system for calculating Lordships, Descendant, Midheaven and Imum Coeli.
And that degree house systems are used for planets.
So for example, Sun might fall into the 8th House but the 9th Sign and under the 9th Lordship.
The whole house system would place Sun into the 9th Sign in the 9th House under the 9th Lordship.
Whereas a degree house system would place Sun into the 8th House, 9th Sign and 9th Lordship.
Take your time with what you believe by looking at both and then taking a few days to look at yourself and work it out.
So Midheaven, Imum Coeli, Descendant and Ascendant all work off the same cross system.
They represent, the 10th house (ambition), 4th house (home), the 7th house (other people) and the 1st house (body).
Technique to figure out what you want to use:
Watch a video on your 4th Lord in _ House, 10th Lord in _ House, 1st Lord in the _ House and 7th Lord in the _ House.
To continue with the example;
If you have 4th Lord (moon; for Aries ascendant, because Cancer = Moon) in the 5th House but the Imum Coeli line for the 4th actually intersects into Leo (sun) because of specific degrees.
You can watch 4th Lord in 5th House, and listen for moon, then listen for sun.
See which feels more right to you about your “home” because the 4th Lord/Imum Coeli = home and mother. Within the 10th Lord/Midheaven video you are interpreting to do with your career, ambition and accomplishments. To do with the 7th Lord/Descendant you are listening about your partnerships, people close to you and your trading systems. The 1st lord/Ascendant you are listening about your body, a strong part of your personality and your first instinctual behaviour.
Good luck :)!