If you look on page 332 of the training manual from 3/25/19 the picture shows a List Item to the right of the Scaling item, and when asked to complete steps 2 and 3 it “broke” the design with a circular reference.
I think that some of the pictures of the items being bigger in scope would have been more helpful, primarily the illustrations on page 332 and 333.
Looking over the instructions and illustrations of the section “Locating the Bottom Surface of the Wheel Bounding Box” it has us create a List Item in Step1 (after the Scale Item previously built); then has us create Bounding Box in Step 4, then a Deconstruct Brep Item in Step6. Making our item chain Mirror >>> Scale >>> List Item >>> B.Box>>>Deconstruct Brep.
Then in Step8 it has us “Connect the output from the Deconstruct Brep B to the input of List Item L”; which, having just crated a List Item in Step1 leads me to connect these Items…creating a circular reference and breaking the equation. If the picture on p.333 has shown the solution with 2 list items (Mirror >>> Scale >>> List Item >>> B.Box>>>Deconstruct Brep>>>List Item) that would have been been helpful, or if we were told to create a second List Item after the Deconstruct Brep Item, that would have been the best. I was bale to see this in looking at the Grasshopper Bike Wheels training file…but it was confusing when the directions left out the second List Item.
So now that we have the confusion of the List Item, and all of that (based on the instruction on p.332 and 333.) coming AFTER the Scaling Item in the chain, when (in steps 2 and 3 of “Scaling the Front Bike Wheel from Bottom” at the bottom of p.333) I was asked to "2. Connect the output from List Item i to the Area m2 G." “3. Connect the Area m2 C to the Input of Scale C or center.” This, again, created a circular reference and broke the equation, because all of this should have been feeding into, not derived from the Scaling Item.
I hope that clear enough and helpful.
And, learning to program in Mastercam came over a long time. Initially I was using it solely for CAM programming and then, slowly, began taking over work from some of the design group that directly related to the manufacturing process, so I could increase my value and free them up to to more deign work.
Thank you and take care,