What is the best way to get the anchor point to the center of a line in Video Copilot for Saber?

[AKASGaming]

I'm trying to make this saber spin from the center while constantly having the anchor point between the two points (Core Start and Core End)

I prefer having to run an expression to do this but if there's another way please let me know!

Thanks in advanced!

PS: I'm using this with this current expression:

x1 = effect("Saber")("Core Start")[0]
x2 = effect("Saber")("Core Start")[1]

y1 = effect("Saber")("Core End")[0]
y2 = effect("Saber")("Core End")[1]

transform.anchorPoint([x1/y1], [x2/y2])

With error: "undefined value used in expression (could be an out of range array subscript )"

[Mylenium]

There is no need to address the property stream name. Those are read-only. Simply writing [x1/y1,x2/y2] would be enough.

Mylenium

[AKASGaming]

So what do I need to edit in my expression?