(a)–(c) Double dot charge stability diagram for the left, middle and right double dot respectively. Using the result of Figs. 2(b)–2(e) the tunnel barriers are set, and the plunger gates are swept as indicated. The occupancy of each dot is denoted by (n, m) corresponding to the number of electrons in the left and right dot respectively of that specific double dot. The algorithm determines how well regions of the charge stability diagram match to a reference cross (see inset). Good matches are encircled. These are interpreted as crossings of charging lines from two dots. The single-electron regime is found by verifying that no other prominent charging lines are observed for more negative gate voltages with respect to the most bottom-left detected cross (green regions). The extra features present in (a) and (c) were below the detection threshold and are attributed to additional dots due to a lack of coupling with the double dot under investigation (a) or a different slope (c). These unwanted dots do not necessarily pose a problem for follow-up double dot experiments. The horizontal scan range of panel (b) is less than for (a) and (c) due to hardware limitations.