Apologies for the confusion on this topic! As Brendan is pointing out, our understanding of these motions have become clearer over time, and we’ve stopped saying “two way pickslanting” to describe this type of scale playing for the time being. When you play a scale, you’re not really “changing the slant”. You’re making different picking motions. Some of these motions involve the forearm joint and appear to rotate. Others that use the wrist don’t appear to rotate. Both of these motions can be used to get over the string cleanly.
A classic example is Andy Wood, an awesome player and good friend of Ben’s, who we’ve interviewed. When Andy plays a fast ascending scale, he uses downstroke escape, or “DSX” wrist motion for the first five notes. This is a type of wrist motion where downstrokes go up in the air, and this is how he gets over the first string change. i.e. The first string is DUD, and during that third downstroke, the pick is in the air, and we can move to the new string. The second string is UDU, and during the sixth note we have to once again switch strings. Because of the DSX motion, the pick would be trapped, so for this, Andy introduces a little forearm motion in addition to the wrist, to lift the pick up and get over the string the second time. Then the pattern repeats.
Because this sixth motion uses some forearm, the arm and hand appear to rotate a tiny amount, creating a semicircular / curved pickstroke that we call the “double escape” pickstroke. And yes, technically, this also changes the “pickslant”, because anything that changes the hand’s orientation will also affect the pick. But I can also change the pick’s orientation in ways that won’t help me get over the string at all, such as by making small adjustments to my grip. So pickslant and picking motion are not the same thing, and many times when players start moving their fingers around to “change the slant” they’re not actually doing anything to change their motion, and thus not doing anything to help their scale playing.
So what we’re really seeing in Andy’s case is that for ascending scales, he uses a hybrid approach: wrist motion sometimes, and forearm-wrist motion at other times. That’s the simplest way to put it. And this approach happens to be very common, used by players like John McLaughlin, Al Di Meola, and many others. Why it’s so common is harder to guess, but it indeed it is.
Interestingly, when Andy descends, there is no forearm at all. It’s all wrist motions, in various combinations. Some of these are downstroke escape wrist motions, which he can use for downstroke string changes just as before. And some of these are upstroke escape, or “USX” motions, which he can use for the opposite string change. Because none of these motions involve rotating the arm, none of these make the “pickslant” appear to change. But the effect is still the same as Andy’s ascending approach. The pick goes over the string on downstrokes, and also on upstrokes.
It’s… complicated! There are lots of ways to do what you’re asking, including playing the entire scale in both directions with no, or very little, forearm involvement at all. Or you can do a hybrid approach like Andy. Considering that great players like Andy are not always super conscious of this blending of motions, one approach to learning wrist motion specifically is to try to ignore them. Instead, follow some instructions for getting any of the core wrist motions happening smoothly, and see if you can intuit the others by feel of smoothness and correctness at medium or better speeds, as Brendan outlines. As you do this, knowing what is supposed to be happening mechanically, and what it is all supposed to feel and sound like when done correctly, is a big leg up compared to tooling around entirely blindly with no knowledge of which motions are which.
And yes the Primer comes with lifetime updates as we integrate more of this type of clarity and teaching into the product over time.
Yes we’re probably stepping away from calling anything “two way pickslanting” at this point, until we’re clear what it even means. As you’re pointing out, the clearest thing to do is look at the motions you’re trying to make.