The most accurate way of measuring the pitch of your web is measuring 10 gaps.
* While the web is in a level position, hook your tape measure over a bar and count 10 gaps. (as diagram)
Pitch of the web in the example diagram is 32mm.
You can also measure the pitch of your web by measuring the distance from one bar center to the center of the bar next to it.
Pitch of the web in the example diagram is 40mm.