I've only seen it mentioned online, I believe it's part of his next level bowling dvd series.
It's has to be used with the figure 8 swing also I believe.
A caveat: this might all be out of context and it's likely there's more to it.
This picture is from the only reference I've ever ran across about it.
In it I believe you draw the long line from your break point through your target arrow, the long line in the "y".
Then you count the number of boards between these two points.
Your pushaway should go the exact same amount of boards to the left of your target arrow, the left red dot of the "y".
This should allow your swing to follow the figure 8 towards your intended exit point.
You might find more about it on youtube, a lot of the next level bowling dvd series stuff can be found on it now.
I don't believe it's used much, it never really mentioned anywhere and there's other systems that are more common (like the 3 point system etc.)
Update:
Did some looking and found this which describes this also:
"Norm duke describes hitting the mark quite well and describes it in depth in his DVD “ learn to bowl competitively “ with his “figure 8” description whereby he aims at the arrows about 15 feet , but isn’t looking at the arrows as such but is glaring at where the arrows are as he is building a spot in his peripheral vision at the break point down the lane, this way he can track his ball trajectory and make adjustments with his swing plane .
The science behind this was if he hits the 25 board arrow and it rolls and breaks at the 4 board then there is a 21 board variance. He adds that to the 25 board (target) which gives him a pushaway target at the 46 board ( basically the gutter cap). He then uses imaginary gridlines to dictate ball speed , up for more, down for less. Then as the lane starts to transition he makes adjustments accordingly."
2nd Update:
Okay here's Norm Video where he explains what he's doing.
It's from Norm Duke’s Learn To Bowl Competitively: Lesson 16: Swing Planes
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