Potential leakage points are avoided, mishandling or loss of loose, unattached parts minimized and installation in tight places facilitated by a meter bar of elongated cast metal structure having a central bar, an outlet conduit section and an inlet conduit section, both integral with the meter bar. This device is a new combination of existing materials configured with unique features that provide an effective, practical and economical way to provide an air blower device. A multiplier multiplies the video signal consisting of N bits output from the analog-to-digital converter by the correction data consisting of M bits stored in the correction value memory, and outputs a video signal consisting of L bits with which the difference in luminance between display pixels on the display is corrected. By a geometrical relationship between the recording device and the imaging system, a deviation of the instrument from the target position is determined. The first switch contact contacts a first test circuit portion and the second switch contact contacts a second test circuit portion in the switch closed position, the first switch contact and the first test circuit portion forming a first air gap and the second switch contact and the second test circuit portion forming a second air gap in the switch open position. Preferably, the transducer is a thermoelectric, piezoelectric or magneto device.