i am looking to buy a house and can see a damp course running 50cm under the bedroom window, why is this? house is 70s built

I would imagine it was a cavity tray fitted when the cavity was closed of prior to the original windows being fitted, should have been cut back a bit. Although not many are fitted now, in the 70s dpc was fitted to sides and under the cill of wooden windows and built in. In response to your edited question, if its not a cavity tray,was there some form of extension/lean to, that has been removed, and flashing just cut of flush with wall, or would it be a sky/tv ariel lead clipped along wall.

How far off the outside ground level is the bottom of the said window? Lets say its a large window and as a rule the DPC should always be 150mm above external ground level! so from the top of this is it by any chance a further 50cm to the underside of the window frame? Scott Cannon.

i assume an extension of some sort has been removed i.e. a small parapet or other and the line you see is where the flashing was its not a d.p.c. its too high up 150mm max plus rising damp will travel max 1metre