1. Add Trendline Right click on data points

2. Modify your graph: 1)Select your graph and copy then paste it so you have 2 identical graphs. 2)Modify the formula bar to select different years. The top graph is 1881 to 2011 and the bottom graph is 1950 to 2011 (in this example 1950 data starts in row 228) 3)By interchanging the Ps with Rs you can switch x and y axes. =SERIES(,Sheet1!$P$228:$P$289,Sheet1!$R$228:$R$289,1)

3. Modify your graph: 1)Select your graph and copy then paste it so you have 2 identical graphs. 2)Modify the formula bar to select different years. The top graph is 1881 to 2011 JJA temps vs DJF temps, and the bottom graph is 1881 to 2011 JJA temps vs year. =SERIES(,Sheet1!$A$159:$A$289,Sheet1!$R$159:$R$289,1)