Which Size is Best? both 12.5" and 8.5" are popular. Decide on the blocks you most often mark and go from there! Many have both!

The Crosshair Ruler is a 12.5" Square Ruler with slots and markings for crosshair marking a quilt block.
Use for 6" - 12" blocks, with 8 slots for crosshair marking and an additional 8 marking, giving the possibility of 16 crosshair markings.
All radiating from a centre point, with 1/2" increments for block sizes.

When quilting on domestic, Longarm, or with embroidery this marking tool is essential. Reference lines give a much better result.

Leonie West, the inventor, says:
Whether quilting on a domestic machine or a long arm machine I like to mark reference lines on my quilts.
Reference lines give me a much better result.

If I am using rotating templates, reference lines will give much more accurate spacing.
On a domestic machine the quilt is not taught as on a long arm machine and there is movement of the quilt sandwich which can make it difficult to use the rotating lines on the templates.
So I mark in the reference lines.
I like using our Cross Hair Ruler to locate the centre and mark 4, 8, 16 and 32 lines if required