I would not use a jig like that because the distance between the pins that the shrouds are tied to will probably not match the distance between the lower deadeyes, making some ratlines too taut and others too loose. A jig like this does not take into account the wider gaps between some pairs of shrouds that exist to make a gap large enough for a gun port to to be clear of obstructions. Shrouds are usually NOT evenly spaced, as shown below.
You don't get that much more working space using a jig like this either. To ensure that the ratlines are the proper length between each shroud from top to bottom, it's best to tie the ratlines on the model.
Use a tool like this, which is clamped onto the shrouds at each step, to keep the vertical spacing even.
The tool not only helps keep the ratline clove hitches in straight, horizontal rows, but also prevents ratlines from being made too tight and drawing the shrouds too close together, distorting them from being straight. With the help of sewing needles, tweezers and/or needle nosed pliers, ratlining is just as easy one the model, and the results are better.
Ratlines are never perfect, but this is the very first ship model I made, and the first set of ratlines, and they aren't too bad. Some of the knots needed adjusting to make the rows horizontally straight, but the shrouds are not pulled out of position, and many of the ratlines have enough slack to form that slightly drooping downward hanging curve which is what real ratlines look like.
When you have moved to the other side of the ship to do ratlines, check the height location of the row you are working on using your machine rule, and compare the left and right ratlines rows to match their heights.