7 years ago I took a Japanese tool class at the Center for Furniture Craftsmanship, taught by John Reed Fox.
This is a simpler version of a project he recommended, combined with the winding sticks that Chris Schwartz recently made.
The big difference is in the dowels that reference the sticks to each other when they're in the vise, so that you can plane the edge of both at the same time, and know that the sticks will be mirror images of each other when you hold those edges together.
John used dovetail keys when he made his, so that they could slide and lock together. But I've been distracted enough by this project, and chose to use dowels as a shortcut.
When held edge to edge, any discrepancy from dead-on straight will be doubled, and you'll be able to see what adjustments need to be made to compensate. Then you can put the sticks back together, and carefully shave down the high spots until your edges are both perfectly straight.
After that, you'll be able to use these sticks to check for wind, as well as to check for cupping and warping.
In theory, you can make them as long as you want. It'll be more work to get them perfectly straight, and they'll be a huge cost savings over something that's precision machined, but these you can fix yourself if they get damaged. And, you can use them to check things like jointer knife projection, without needing to worry about nicking the knives.
It's an entertaining but small project, and a good exercise in precision planing. And the inlaid bits do seem a lot easier to read than a long, solid stripe.