The principle of metrological support in technosphere safety is considered. It is based on practical metrology. Theoretical aspects of accuracy and errors of measuring instruments intended for diagnostics and control of the technosphere under the influence of factors harmful to human beings are presented. The necessity of choosing measuring devices with high metrological characteristics according to the accuracy class and contact of sensitive elements with a medium under control is shown. The types of additional errors in measuring instruments that arise when they are affected by environmental influences are described. A specific example of the application of analyzers to control industrial emissions and measure the oil and particulate matter in wastewater is shown; it allows accessing advantages and disadvantages of analyzers; and recommendations regarding the missing metrological characteristics of the instruments in use are provided. The continuous monitoring of the technosphere, taking into account the metrological principles is expected to efficiently forecast the technosphere and make appropriate decisions.