The Model TBM300 Portable Opacity Meter consists of two basic units connected by a single cable. The sensor unit is installed end-of-line on the exhaust outlet of the vehicle under test and contains the light source (green led) and receiver (photo detector) modules. The sensor head is a cast aluminum (black anodized) housing to provide a stable housing for the Model TBM300 optics. The control unit is battery powered with an alpha numeric membrane keyboard, large LCD display, internal printer and RS-232 data output. The control unit implements software programs to provide many functions required to perform diesel smoke tests. Because more and more local agencies require varying acceptance levels of smoke, the Model TBM300 provides keyboard modification of pass/fail limits.