filling in space between 2 series

Hi this is my first time here. I am an excel novice.
I have a chart where i plot 2 series against time. The one series being good voltages plotted in green and the other series being voltages out of tolerance plotted in red. My problem is lets say the voltage good level is 3. If on Tuesday the reading is 5 it is good and is in the first series. On Wednesday the reading is 0. It is in the second series so there is a gap in the graph from where the green ended at 5 on tuesday and it started in red at 0 on wednesday I need a way to insert a fictictious point at 3 in both series so it will connect.
Any ideas...
Thanks.
Lewie

Could I make 2 series with the same numbers and make them visible according to a formula or value