> I'm getting ready to s&g the keel of my first kayak ever, I can figure out
> how to stitch it & how to glue it, but I still don't know how will I
> be able to mesure it's simmetricity. In other words: I want to make sure
> the keel is simmetric before gluing it. I'm sure it will not be simmetric
> on the first shot, it's my first kayak, & I'm not that perfect. I will
> be able to fix it if I'll be able to measure it.

I agree with Don. Additionally, you can be nearly certain before you start if you clamp the two keel halves together temporarily and trim the edges of both together at the same time. Fasten them together with inside faces together (or outsides together, it doesn't matter which), then plane and sand to final dimension. You will now have to pieces that are mirror images of each other, and which will nearly always be symmetrical after assembly.

To check straightness, clamp a stringline from the topside of the assembly, running from the joint between panels right at the bow to the stern, and eyeball it carefully after you insert the wires but before you wet out the tape. Adjust wire tension if necessary to fair out kinks and wows. Your eye will pick up variations that are nearly too small to measure.