Adjusted: Often times watches will have the word "Adjusted" engraved on the movement. Such watches are generally of a high grade. Adjusting refers to the watch having been corrected for timing errors due to temperature changes and also for positional errors.
High Grade: A watch of high quality. The movement is usually marked " adjusted" and is well finished. The movement has a least 17 jewels, often more.
Isochronism: Occupying equal time. In theory, a perfect balance wheel would complete a large arc in the same amount of time as a smaller arc. In practice, this is not the case, and it is one cause of positional errors.
Movement: The actual mechanical part of the watch inside the case excluding the dial and hands.
Positional Errors: Both gravity and friction have an effect on the rate of a watch. In the pendant positions, that is with the dial vertical, the existence of a even a very small heavy area on the rim of the balance wheel will cause the watch to run faster or slower depending upon the location of the heavy area and the particular vertical position--pendant (or winding crown) up, down, right or left. For example if, because of a positional error, a watch runs fast with the pendant up, it will run slow with the pendent down. The same with the right or left positions--if fast in one direction, it will be slow in the other. The correction is to poise the balance wheel, which means to eliminate the heavy area either by adding weight to the balance wheel rim opposite the heavy area or subtracting weight from the heavy area. Friction increases in the pendant positions compared to the dial positions, that is the watch flat either dial up or dial down, causing the balance wheel to swing in a smaller arc. This may either increase or decrease the rate depending upon a number of factors. See isochronism.
Temperature Error: Variations in temperature cause timing errors which must be compensated. Temperature compensation was particularly important in older watches before the widespread use of metals for balance wheels and balance springs of alloys with very small coefficients of expansion. Typically with a rise in temperature, the balance wheel will increase in size which will slow the rate of the watch. The balance springs will become weaker which will increase the rate of the watch. Unfortunately, these opposite errors do not entirely cancel each other. The larger balance wheel will only slow the watch a few seconds a day, while the weaker balance spring will cause the watch to run perhaps a minute a day faster.