WinterMoon said
An equal house chart has no 10h cusp MC, because equal houses are flat equally divided spaced houses based on the ASC degree following around in sign order. The 10h cusp on a calculated chart is also its MC and the 4h cusp is the IC. The midheaven marks the highest point where a planet culminates in the sky for that chart's time and place. But equal house still has to be calculated to get the ASC degree which is then  used around the chart following in sign order as equal houses. The calculations to get the ASC degree results in the calculation for the houses and the MC...but equal house uses no 10 cusp MC or calculated houses because equal houses are divided equally and evenly spaced based on the calculated ASC degree. If the calculated MC is placed in an equal house chart, it is not on a cusp and does not change signs because it is the calculated MC based on the time and place of birth, it represents the MC which marks the calculated angle point where the planets reach their highest point in the sky in a calculated chart. This is seen visually at local noontime sky when the Sun is at its highest point at the MC and from there on it starts to head for setting. It' s like an equal chart is flat showing an uncalculated, equally divided circular Earth horizon with the planets placed around it, and the calculated chart circular Earth horizon houses are showing more dimension by showing height and depth along with the rising and setting places of the planets and stars in the sky viewed from Earth based on an accurate birth time and place. If an equal house chart includes a MC, it does not change signs because it is not the 10h cusp of the equal house chart, it is the calculated point of the actual MC based on the time and place of the birth chart, as is the ASC.

  

Does that mean there would be different interpretations for a "ninth house MC", "tenth house MC" etc? 

No, the MC is the culminating degree where a planet reaches its highest point of rising based on the time and location of that calculated chart and coincides with the cusp of its 10h.

In a calculated chart the MC is an Angle. The equal house system of repeating the ASC degree around in sign sequence in divisions of 12 equal houses has no MC/IC Angles even though a MC degree is sometimes shown placed in it. The MC degree is derived by calculation but equal houses are equal areas, therefore an inserted calculated MC degree placed in an equal house chart sits where it fits, it appears to be in a house, but the equal houses are divided houses not calculated houses and the MC being an Angle is not read as being in a house. The MC Angle is not read as being in a house in a calculated chart either even though it coincides with the 10h cusp, nor is the ASC rising sign degree for that matter, it coinciding with the 1h cusp.

WinterMoon said
No, the MC is the culminating degree where a planet reaches its highest point of rising based on the time and location of that calculated chart and coincides with the cusp of its 10h.

In a calculated chart the MC is an Angle. The equal house system of repeating the ASC degree around in sign sequence in divisions of 12 equal houses has no MC/IC Angles even though a MC degree is sometimes shown placed in it. The MC degree is derived by calculation but equal houses are equal areas, therefore an inserted calculated MC degree placed in an equal house chart sits where it fits, it appears to be in a house, but the equal houses are divided houses not calculated houses and the MC being an Angle is not read as being in a house. The MC Angle is not read as being in a house in a calculated chart either even though it coincides with the 10h cusp, nor is the ASC rising sign degree for that matter, it coinciding with the 1h cusp.

  

Thanks. But it still has meanings traditionally associated with the tenth house? Or are the more prosaic career type questions interpreted into the (equal) tenth house with the more esoteric, spiritual or psychological themes remaining with the MC?

The MC and IC calculation to my mind is what gives more cred to the Placidus method.   Though it could just be that I'm used to it and seeing the MC before the 10th house looks odd for now.

I prefer Equal. I used Placidus for many years before realizing Equal is better and more accurate. No one swayed me to switch either- I found out on my own. For many years I assumed Placidus was the best because it was Astro . coms default. It’s really not, imho.

I realized this because my Mars changes from  9th in Placidus to the 8th in Equal. I wanted to believe I had a 9th house Mars for a long time but the fact is whenever I have any type of transit to Mars, I do not experience anything related to the 9th house... I don’t travel or pursue higher education or anything like that. I experience more intense 8th house psychological type of experiences- intense power conflicts and pursuing more occult type of interests. When my Mars is activated by transit, I am more interested in psychology and more inside my own head. The 9th is more out there —->as in engaging with the world and broadcasting. 

I do have a 9th house Venus, and when it is activated by transit, I have 9th house experiences. This is how I was able to compare. 

The MC is the calculated DEGREE of the highest place a planet reaches for that particular calculated chart, its based on the coordinates of time (longitude) and place (latitude) for the chart. The association with the 10h is that the highest point of the Natural Chart is based on the solar year of seasons and the Natural Chart 10h cusp (00°00"00' Capricorn) is the beginning of the seasonal solar year in the northern hemisphere, which lends its meanings to both hemispheres. The axis delineation of the calculated angles of IC/MC are associated with the calculated cusps and houses of 4 & 10. The equal house 10 is not associated with a MC.