Either the nine or ten degree ruler will work, and they both use the same fabric requirements. The runner is a bit longer with the ten degree ruler, if you want it shorter leave of the first wedge ruler cuts 21 3/4" and it will be shorter, or cut them all and unsew the first ones when it is time to connect the two halves if it is too long for your table
Patty Latourell
Spicy Spiral Table runner designer
[email protected] if you have more questions, be sure to put a reference in the subject line about Spicy Spiral