Figure 3 is a line graph that shows total solar output in W m-2 on the y or vertical axis against year on the x or horizontal axis (from 1850 to the current time). The graph shows two lines which have several peaks and troughs, illustrating oscillating data.
The first (a blue line) represents the Krivova/Ball dataset with the output oscillating around a constant value of around 1361 W m-2 from 1850 to 1940, with a peak to peak range of about 0.4 W m-2. There are 4-5 oscillations per 50 years. From 1940, the pattern continues, but oscillating around a higher mean level of about 1361.5 W m-2, and a larger peak - to peak range, of about 0.7 W m-2. This pattern decreases a little over the period from 1960 to 2000.
The second line (a red line) represents the PMOD data set for the period from 1978. This follows a similar oscillating pattern to the Krivova/Ball line, but with lower values to the blue graph and decreasing a little over that period.