Measuring the earthshine signals ΔI,   ΔQ for relatively low (phase 73°, region #1, filter B) and high (phase 98°, region #1, filter R) moonshine levels with the background x′ and measuring regions x indicated. The dashed lines illustrate the guessed level of the background (mainly stray light) and background plus constant earthshine regions (reflected from maria). The full line is the linear extrapolation of the measured background from the x′ to the x region.