In Surveyor 2.0, Pick the track icon in the asset panel on the left and then put ruler in the search field. In Classic, it is on the Objects panel, click on the right box at the top of the panel to enter spline mode. Then change the yellow text to read ruler.
Sorry I just checked and this sentence should read In Surveyor 2.0, Pick the Scenery Spline icon in the asset panel on the left and then put ruler in the search field.