Reduction of measurements of total Solar flux to unified scale and uncertainty in estimation of its long-term trends

A comparison analysis of measurements of total solar flux in ACRIM and PMOD scales was made. The analysis of integrated differences of solar flux simultaneous measurements allowed us to estimate systematic distinctions which can result in accumulation of significant errors. The solar flux measurements in ACRIM and PMOD scales are reduced to the intermediate radiometric scale by data correction for systematic errors. Corrected measurements in the unified scale are consistent and represent a compromise between original data sets. Measurements in the intermediate scale demonstrate changes in solar flux between solar activity maxima in 1986, 1996 and 2008. The amplitude of these measurements is comparable to uncertainty in their long-term trends that calls into question estimations of secular variations of solar luminosity which were obtained before.