I have been attempting to fix a dado rail from the horizontal to go up the stairs, but try as I might I can't seem to get the angle right for the join. Ay help would be much appreciated, before I LOSE ALL MY HAIR!
I am not quite sure what a Dado rail is but I am assuming it is a trim or molding type from your description of your problem. I am not a carpenter (I would have probbly known what it was). But I have used a trick of mine many time to find the angle for trim. Take a sheet of paper put at the intersection and draw a line horizontal with the wall on it and then the angle of the rise of your stair case. After your lines are drawn you have the total angle of the joint! To find the angle of your miter you will cut off the excess paper and fold it so the lines meet.