# How to draw guide lines spanning between two panels or graphs?

I would like to draw the blue guide lines as shown spanning between the top and bottom graphs. Any help is appreciated. Thanks!

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Please add any germane code to generate the graphs and clarify precisely how these "guide lines" are defined. –  ciao Jun 1 '14 at 22:27
Kuba answered. (Graph is generated in xmgrace and not mathematica.) –  Ari Jun 1 '14 at 22:55

The key is PlotRangeClipping-> False:

With[{stdopt =
Sequence[Frame -> True, Axes -> False, ImageSize -> 300, PlotRangeClipping -> False,
PlotStyle -> {Red, Thick}]},
Column[{
Plot[x, {x, 0, Pi/2}, Epilog -> {Thick, Blue, Line[{{.5, .5}, {.5, -1}}]}, stdopt],
Plot[Sin[x], {x, 0, Pi/2}, stdopt, Epilog -> {Thick, Blue, Line[{{0, Sin@.5},
{.5, Sin@.5}, {.5, 5}}]}]
}, Spacings -> 0]]


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You may be also interested in PlotRangePadding->0. –  Kuba Jun 1 '14 at 21:52
It's the Epilog which did the trick. Very nice! –  Ari Jun 1 '14 at 22:52