Using the ASTM D4400 standard, using the paint sag resistance test method, this is a drop vane with a series of successive high gaps. The notch gap is related to the degree of sag and provides a value called the anti-sag index. The higher the anti-sag index, the better the anti-sag performance of the coating. The development of this instrument and its versatility for control and research have been described in published reports. Official Digest (JCT), October 1962. Official Digest (JCT), January 1964. Sag Testers are known as ASTM Method D 4400 and Federal Fed, Method 4494 Test Method No. 141 and are an essential piece of equipment in paint laboratories in the United States and around the world.