The most common cause of a lack of curve is the measurement not being taken from the whole arc or full extension of the rafter.
The steps to measure the curve are included below and there are some photos to guide you.
Please note: It is very important that the curve of a rafter is measured when it is fully locked in its extended position.
To check the curve of your rafter:
1. First, make sure it is fully extended to its maximum length.
2. Then tighten the knob as tight as it will go, this will form the arc
3. Lie the rafter down with the two ends against the ground so the full arc can be seen.
4. Then measure the curve from the middle where the knob/nut is
5. The curve is taken from the ground to the top of the rafter. This is the arc (photo attached)
It's also important to note that the curvature is measured when extended and includes the distance from a flat surface to the top of the rafter (note the rafter is approx. 35mm tall), as per the above instructions. Variation will occur depending on the amount of extension. A small amount of variation can also occur in production.