A
Abrasive Cutting Master (ACM)	The tool used in the total form machining method of producing graphite electrodes.
Altered Metal Zone (AMZ)	The mechanically and mechanically altered zones created by the EDM process on the workmetal surface.
Ammeter	An instrument for measuring electric current in amperes.
Amperage (A)	In EDM, the amount of average current measured during the cut.
Ampere	The unit of electric current. Equivalent to the steady current produced by 1m, volt across 1 ohm.
Angstrofine	A class of EDM graphite characterized by a particle and pore size of less than 1m very high strength, isotropy, and uniform structure. The most advanced graphite material available.
Anisotropic	Exhibiting properties whose values change when measured along differing axes. Opposite of isotropic.
Anode	The positive terminal of an electrolytic cell or battery. Often incorrectly applied to the tool (electrode) in the EDM process.
Arc	A continuous flow of electrical current between an electrode and workplace. Should an arc occur in EDM, the workpiece, electrode, or both will usually be damaged. An arc is normally visually recognizable as a yellow flash.
Arc dampener	Same as Arc suppressor (below).
Arc guard	Same as Arc suppressor (below).
Arc suppressor	A circuit in the EDM power supply that reduces the possibility of arcing.
Automatic Tool Changer (ATC)	A device used with computer numerically controlled EDM to provide automatic operation.
Automatic depth finder	(Refer first to Depth finder) An automatic depth finder is electrically connected to the servo and will stop the downward advance of the electrode at within 0.0001" of the workpiece surface and will hold it at this distance. Therefore, if the workpiece position is shifted by moving the table in any direction with its handwheels, the servo will constantly adjust the vertical relationship of the electrode to maintain its distance at 0.0001" away from even a previously EDMed cavity, even one with an irregular surface.
Average current	The average value of all the minimum and maximum peaks of amperage in the spark gap, as read on the ammeter. For any given available current setting, the higher the average current, the greater the efficiency of the particular cut being made. See Machining rate.