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Go to Project Settings > Expressions and make sure the engine is set to JavaScript.
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Name it Guide.
Hold Shift and parent the text to the Ellipse. Parent the Ellipse to the Guide.
Name it leadingSize.
var leadingSize = thisComp.layer("Guide").effect("leadingSize")("Slider");
style.setLeading(leadingSize);
var textSize = sourceRectAtTime();
[textSize.left + (textSize.width / 2), textSize.top + (textSize.height / 2)];
This makes the Anchor Point auto adjust to the center, left is how far the left edge is from the Anchor Point, adding half the width gets you to the middle of the box, same logic applies for the top and height.
Name it numberControl, this will control how many numbers are shown.
Set units to index. Based on lines. Smoothness to 0. Scale to 0.