Existe uma maneira de fazer isso que não é bonita, você terá que adicionar uma série fantasma com dois pontos de dados.
You can set XY scales proportionally without macros, but using additional chart series consisting just of two data points to plot a diagonal line with equal tangents. The tangent length shall be dx=max(x)-min(x) or dy=max(y)-min(y) whichever is larger. Based on tangent length Excel will automatically set equal (or almost equal) limits to X and Y axes.
Step 1: Plot area shall be square (you can do it manually or in VBA (see IRstuff postage) ActiveChart.PlotArea.Select Selection.Width = 400 Selection.Height = 400
Step 2: Reserve 2x2 range for new series. Using IF function enter formulas for xo and yo
if dx >= dy
xo(1)=min(x) yo(1)=(max(y)+min(y)-dx)/2
xo(2)=max(x) yo(2)=(max(y)+min(y)+dx)/2
if dx < dy
xo(1)=(max(x)+min(x)-dy)/2 yo(1)=min(y)
xo(2)=(max(x)+min(x)+dy)/2 yo(2)=max(y)
Step 3: Add new series to the chart. Set line and marker width to none to make chart invisible.
O usuário que fornece a resposta tem um link para o software SectProp .