Ever thought about buying a centre ruler? Print these paper ones out first, to see how they work and try them out.

Printable Adjustable Centre Rulers - Metric

You can enter the work width to draw the 2 edge lines on the ruler, to make it easy to align, and add number of divisions to mark the ruler at each division point.
To print a ruler wider than a standard A4 Landscape (297mm), it also creates 2 separate, opposite rulers you can print, cut and tape together to get up over 500mm.
Please let me know if it needs additions, edits or fixing.

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