In the top panels (left abscissae), the black curves are plots of the normalized blue wing signal/red wing signal ratio observed by GOES-16 and GOES-18 EUVS-C On August 9, 2022. Red curves are 30-minute-long running averages that track the diurnal variation of the ratios. Blue curves (right abscissae) are black-red. Their standard deviations (σ_b/r = 3.1 × 10⁻⁵ and 2.4 × 10⁻⁵) for GOES-16 and GOES-18, respectively, are measures of the random error in the blue/red ratios after removal of diurnal trends. The bottom panels are plots of the h line/k line ratios (black) and 3-minute running means (red), along with the differences (blue). Their standard deviations are σ_h/k = 2.5 × 10⁻⁴ and 1.9 × 10⁻⁴. Values for both σ_b/r and σ_h/k are consistent with the errors calculated using equations (9), (11), and (17). Larger values for GOES-16 reflect its relatively larger loss of radiometric sensitivity with solar exposure (Sect. 4.2.4).