That's where I thought a base with a spline might work almost like a tape measure. Stretch up from wherever it's place to the height we need. There could be two versions, one in imperial and one in metric to satisfy the itch of whoever uses it.I only know of 5 assets that act like a vertical ruler and they have issues. The main problem is what Peter points out that they measure from the baseboard surface in most cases and they are on the real world scale of around 100 feet. However, if they are height adjustable then you can measure relative height such as the clearance under a rail bridge. If you model real scale then you might not need to know relative heights but many model railroad plans have heights measured relative to the low point or to the floor. Trying to get the heights correct so that the grades are correct can mean a lot of fidgeting.