Level Use To get a correct reading with a level, both ends of the bubble should be viewed. If the gaps between the ends of the bubble and the lines are unequal at any time, then they should be averaged out. The reason for this is temperature, which affects the size of the bubble. As a level is warmed the liquid expands, thereby reducing the size of the bubble so that at true-level there will be gaps at both ends between the bubble and the reading lines. Conversely, if the temperature is very cold, the bubble could expand and overlap the reading lines. Excessive hand heat on the center of the level for an extended period of time could expand the center, causing the working surface to become slightly convex and also create a tendency to spin on flat surfaces. This is more noticeable on very precise levels. Any level can be checked for accuracy on any flat surface regardless of whether it is level or not. Simply put the level on the surface and note the position of the bubble. Then reverse the level in the same spot. If the level is true, the bubble will be in the same relative position both ways. Some models, like our 98 machinist levels with an adjustable system, have an adjustment that can be made on the job. Level Vial Informa tion The accuracy of a level is dependent on the proper machining of the working surface, the straightness, and rigidity of the construction and the sensitivity of the level vial. Accuracies are very often specified in parts of degrees such as 10-second accuracy or 43-minute accuracy. Technically, we are referring to the sensitivity of the level vial, but many interchange these terms. Since this means little to most people, we use the more practical definition of inches per foot of elevation. For instance, a 10-second vial accuracy means if the level is on an incline that is .0005" per foot, then the bubble on the vial will move .100" (slightly less than 1/8"). There are three general types of level vials. Ground vials are generally used in precision levels; bent glass and plastic vials are used in most other levels. Most level vials have just two lines spanning the length of the bubble because most users just want to know if something is level or not. The more precise levels have vials with a number of reading lines on each side of the bubble. All Inch reading vial graduations are .100" apart.This will show the machinist in a very precise manner how level the equipment is. Metric reading levels have vial graduations 2mm apart and accuracies are usually described as millimeters per meter. This is an easy conversion to make, so we converted our Inch specifications to an understandable metric reading. Machinists only need to know how far they are out of level if the bubble moves to the next line. 199, 98 and 132 Precision Machinists' Levels These are the finest levels available, used for precision work that is typically required in the industry. They all have these features: • All level bases are made from the finest quality seasoned cast iron and are precision-machined on the reference surface • Non-machined surfaces have an attractive, black wrinkle finish • All models except the 199 have an involute longitudinal groove between the bearing flats for accurate seating on round work. This groove has a special involute design, permitting better centering and greater capacity to handle larger rounds • Groove and bearing flats are machined together for maximum accuracy 199 Master Precision Level 15"/380MM The efficiency of modern, high speed machinery depends to a large degree upon the levelness of the machine set-up. • Specially designed to set up, check and test machinery of all types • At-a-glance reading of the exact variation of machinery levelness • Ground and graduated main vial of 10-second accuracy; one division equals 1/2 thousandth of an inch (0.0005") per foot, or 0.04mm per meter • Main vials have seven graduations on each side of the bubble • Auxiliary level vial shows lateral position and assists in horizontal setting • Level vials are positioned so breakage is reduced to a minimum • Special alloy iron used to obtain freedom from thermal effects • Seasoned, machined castings • Scraped reference surface • Nonconductive top plate and black wrinkle finish on nonmachined surfaces • Finished wood case Master Precision Levels 199 Master Precision Level Cat. No. EDP Length Base Width Base Height Level in mm in mm in mm 199Z 50719 15 380 1-5/8 40 3 75 199Z W/SLC* 66932 * Includes redemption card for Standard Letter of Certification (SLC). 199Z 370 M achinists ' L evels