Ultrasonic flowmeters of liquids have been used each more time in fiscal measurements due to it low uncertainty of measure. That meter uses the methodology of transit time, the relationship between the measured speed and the flow was made through the warranty of flow profile, usually denominated profile of completely developed. As in practice distortions of this profile exist, the use of several acoustic bunches can compensate the discrepancies, doing with that the flow measurement has a lower uncertainty. The Oficial Document of ANP/INMETRO determinated that the fiscal flowmeters of liquids should be calibrated at least every 60 days, unless the measurement report demonstrate that other interval among calibrations is feasible. Recently, a larger interval was proposed for the ultrasonic flowmeter of 5 channels (4 years), associate to the warranty of acting of the meter and of the maintenance of the flow profile among calibrations. The aim of this work is the proof experimental that the measurement diagnosis and maintenance of flow profile is an important tool for the warranty that the liquid flow is being measured correctly and inside of the requirements of fiscal measurement determinated by the actual legislation. This way, a system of acquisition of data was coupled to the ultrasonic flowmeter of 5 channels, then the meter calibrated in two laboratories certified by INMETRO and belong Brazilian Calibration Network, respectively with water and mineral oil registering these reference values, also used for a comparison among the metrological characteristics of the two laboratories. After, the meter was install in a platform, demonstrating that the metrological characteristics was maintains after it installation. Finally, a day of production of the platform was monitored, being obtained information about the reliability of the measurements and of it uncertainty.