URGENT REQUEST: Button Hole Spacing

THIS IS AN URGENT REQUEST RE: VOGUE 8872

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I’m currently sewing vogue 8772 (view E) but I’ve come to a road bloc as it seems I’ve lost a piece of my pattern! The piece is a guide to show the sew-er how far apart to space the buttons and button holes down the front of the blouse.

QUESTION: Is there a rule of thumb for spacing buttons on a blouse?

Please help, this is the first blouse I’ve made and I’m quite stuck! All suggestions appreciated