about dotplot legend meaning Here is the code I used:

DotPlot(object = cluster, genes.plot = c("Hcn4","Shox2","Nkx2-5","Nppa","Tnnt2","Gja5","Tbx18","Tbx3","Isl1","Scn5a","Cacna1d"),  plot.legend=TRUE)


I was confused about the legend with the Negative number shown for avg.exp.scale. Does it mean that the cluster expressed the genes at low level or that gene was down regulated? (like the Shox2 in the "0" compared with "2").
The expression values for each gene are scaled / standardized by subtracting the genes mean expression and dividing by its standard deviation. A value of -1 would imply it's one standard deviation below the mean expression for that gene.