Does anyone know how to put in reference lines in charts?

[Bharat]

I am trying to chart my blood sugar. In the charts, I am using:
(1) Less than 140
(2) Between 140 and 160
(3) Higher than 160.

Is it possible to put in reference lines at 140 and 160 of a different color
so when I plot my blood sugars for after luncha nd after dinner, wherever the
points on the curve are, should tell me graphically in which of the three
areas the points are.

Thank you for all your help.

 

[David Biddulph]

Add a couple of new series to your data sheet:

X=Xmin, Y=140
X=Xmax, Y=140

X=Xmin, Y=160
X=Xmax, Y=160

Add those 2 extra series to your graph.