I found (theoretically) a better way to do it in Solar Fire, and I found an interesting chart to demonstrate - It's the upcoming Canlunar, where I just happened to have Vertex turned on as a display point when I popped it up. I got quite a surprise, so I'll offer it as an example. If you want to follow along, the Canlunar occurs December 15, 2016, 11:49 PM EST, Washington, DC.

First a reminder of what the Vertex is: The Prime Vertical is a great circle that rises due east and sets due west, passing directly overhead and underneath,

*i.e.,*through the Zenith and Nadir. The plane of the Prime Vertical is always at right angles to

*both*the plane of the horizon and the plane of the meridian. Where the ecliptic crosses (intersects) the Prime Vertical, we mark the Vertex (on the west side) and the Antivertex (on the east side). If contacts to the Vertex are to be measured mundanely (as with all other angles), the question is how to do this.

**#1. Zodiacal Conjunction**

Contacts could be taken just by ecliptical longitude. This would be different from the way any other angle works, but I mention it because it's how Vertex contacts have been taken historically, and is at least a possibility. (I allow a maximum 3° orb for Vertex contacts.)

In this case, Neptune is 1°19' from conjunct Vertex in longitude. In contrast, Mars is 10°32' in longitude from Vertex. (Why do I even mention Mars? You'll see soon.)

**#2 Azimuth**

The way I have been estimating mundane contact with Vertex so far has been realizing that a planet on Vertex or Antivertex if conjunct Prime Vertical, meaning that the planet is on the due east / due west axis. This means it has an azimuth close to 90° or 270°. Solar Fire shows that, in the sample chart, Neptune has an azimuth of 268°47' and - surprise! - Mars has an azimuth of 271°59. Both are close to 270°. In experimentation over the last year or so, it seems that about a 5° variance in azimuth is more or less about where a 3° orb in conjunction falls.

**#3 Measure Around the Meridian**

This would be the purest way, I think, but we don't have a way of doing it. That is, in the same way that we measure proximity to horizon or meridian along the Prime Vertical (which is at right angles to them), we could measure proximity to the Prime Vertical along the meridian. However, we don't presently have a tool for this.

**#4 Prime Vertical Amplitude**

I just discovered we have this option. It is the distance above or below (actually, north or south) of the Prime Vertical. It is analogous to altitude above and below the horizon. Now, here's the cute thing: When dealing with bodies that are close to the horizon, altitude is always nearly identical to distance from the horizon along the Prime Vertical! Similarly, PV amplitude, for bodies that are close to the PV, would be very close to (nearly identical to) measuring the distance along the great circle of the meridian as mentioned in #3.

In Solar Fire, under "Harmonics, Transforms & Analogues," we calculate PV longitude (mundoscope positions) using "Z-Analogue Prime Vertical." Immediately under this is "Z-Analogue PV Amp." This is the value we want. Calculating this chart, the Vertex and Antivertex will always show as 0°00' Aries (just as a convention). We see that Neptune is 1°11' on one side of the PV, and Mars is 1°49' on the other side.

I think this is the correct way to calculate distance from the Vertex axis, in the same way that altitude is a valid measurement of distance from the horizon.

Along with all of this, we also learn that planets can look like they're a long way from the Vertex (like Mars 10° away in the sample chart) and actually be very close. Mars is as close to the Prime Vertical circle as Neptune, and that's with not much celestial latitude. This alerts us to a whole new dimension of looking at the Vertex.

I submit that, at this point, we don't know whether contacts to the Vertex axis should be mundane or zodiacal, though every other angle works mundanely and one is, therefore, inclined to start with the assumption that the Vertex works this way too.

I might have to look at this Mars placement on Nova's mapping method to better see, geometrically, what's going on.