A tool is provided for calculating the length and number of filler design elements to be used to eliminate an irregular gap in a wall being covered with cast veneer wall panels having a series of repeating design elements. The tool includes a ruler having gap measurement, length of cut and number of filler design element scales. The tool also includes a medial slide carried on the ruler. Two measuring points are also provided. The first is carried on the ruler. The second is carried on the medial slide.