The Model 205 Dual Beam Ozone Monitor makes use of two detection cells to improve precision, baseline stability, and response time. In the Dual Beam instrument, UV light intensity measurements Io (ozone-scrubbed air) and I (unscrubbed air) are made simultaneously. Combined with other improvements, this made it possible to reduce the time between ozone measurements to 2 seconds, making our instrument the fastest UV-based ozone monitor on the market, while still retaining the small size, weight, and power requirements of our popular Model 202 Ozone Monitor. Fast measurements are especially desirable for aircraft and balloon measurements where high spatial resolution is needed. Alternatively, one can choose to average more points internally to obtain even better precision. Flash card memory and a long-life, quiet internal air sampling pump are now standard on the instrument. The Model 205 Dual Beam Ozone Monitor has been approved by the EPA as a Federal Equivalent Method (FEM) based on a modification of the Model 202: EQOA-0410-190.