model. The profile projector is hence widely used in precision machinery manufacturing, including aviation, aerospace industry, watches and clocks, electronics, instrumentation industry, research institutes and detection metering stations at all levels, etc. Work principle The projector magnifies the profile of the specimen, and displays this on the built-in projection screen. On this screen there is typically a grid that can be rotated 360 degrees so the X-Y axis of the screen can be aligned with a straight edge of the machined part to examine or measure. This projection screen displays the profile of the specimen and is magnified for better ease of calculating linear measurements. An edge of the specimen to examine may be lined up with the grid on the screen. From there, simple measurements may be taken for distances to other points. This is being done on a magnified profile of the specimen. It can be simpler as well as reduce errors by measuring on the magnified projection screen of a profile projector. The typical method for lighting is by diascopic illumination, which is lighting from behind. This type of lighting is also called transmitted illumination when the specimen is translucent and light can pass through it. If the specimen is opaque, then the light will not go through it, but will form a profile of the specimen. Measuring of the sample can be done on the projection screen. A profile projector may also have episcopic illumination (which is light shining from above). This is useful in displaying bores or internal areas that may need to be measured. Features Projection methods Vertical projectors: The main axis is parallel to the plane of the screen. They're most common, and suitable for flat parts or smaller work-pieces. Horizontal Projector: The main axis is perpendicular to the plane of the projection screen. Screens are thus made mainly in medium and large versions generally suited for examining shaft parts or heavy work-pieces with large profiles, although having a horizontal table below without a hole for light transmission can be convenient for small machines with a silhouette lighting arrangement. Positive or inverted images For the simplest type of profile projector, the part's inverted image, also known as its mirror image, will be displayed on the screen. In order to facilitate the measurement, sometimes a plus-image system is deliberately added, changing the inverted image into a positive one, which increases the cost due to