Top: 2D histogram of the number of positive sources detected in all the data cubes when searching for emission lines using SoFiA2. The x axis represents the S/N of the line and the y axis shows the number of channels spanned by each detection. Bottom: fidelity grid derived from Eq. (1) considering the number of positive and negative sources found for a given combination of S/N and number of channels. Values close to unity represent the highest fidelity, while zero represents the least reliable parameters. Lines with S/N above seven and spanning about seven channels usually have high fidelity values, i.e. beyond the grey lines of both panels.