Comparison of solar UV irradiance in the 240–260 nm integrated region. SORCE covers 17 years of operations that overlapped for 2 years with the new TSIS-1 SIM measurements. The time period covers the decline of SC23, the full SC24, and the ascending phase of SC 25. Clear large differences in the UV variability in SC23 are obvious for the comparative measurements of SORCE SSI instruments. While SOLSTICE shows a variability consistent with both proxy-based and model UV irradiance variability predictions, the SORCE SIM variability appears to have large uncertainties in the instrumental degradation corrections (consistent with being under-corrected here). The new TSIS-1 SIM measurements – with significant improvements in signal-to-noise performance and stability corrections – are showing the last activity features of SC24 and the beginning increases of SC25. The SSI values for all instruments are plotted on their native reported irradiance scales.