I'm in the process of designing a launch pad and have been looking for some type of bubble level(s) to install on it in order to align the rod or rail to true vertical by adjusting levelers on each leg of the pad. I was in Walmart earlier this evening looking for something else and came across these trailer levels. I found them in the trailer/RV section and were just what I wanted. The price was $5.97 for two of the levels. By mounting them on the pad and they will allow me to adjust the pad right to left, and front to rear. The marks are at approximately 1 degree increments, and by adding an extra imaginary mark at each end of the level they are good for about +/- 5 degrees. I thought I would share this in case anyone would like them for their launch pad.