It is Not measured along the slope, it is measured on a level horizontal plane.

Here's a good rule of thumb that my custom shower door guy told us on our jobs: With standard thickness of glass ( I believe 1/4" to 3/8" thick) the price was $280 to $380 per every one foot horizontally, not vertically, on swinging shower doors (not sliders).  

The dog frequently reacts to any of my activity near the fence and barks and lunges at the fence where the lower horizontal rail has been bulging outward for a long time.

If you have brick, modernize the look of the front by using 1x8's, horizontally and spaced about 4" apart as the surround for the deck. 

Cast iron and copper are still mandatory for plumbing drain/waste/vent on buildings taller than 40'  Getting back to old galvie supply piping....the water pressure is usually rendered adequate when just the horizontal piping in the basement is replaced.

Would you rather use your capital to build out and maximize your investment, or continue purchasing other investments (go horizontal with more properties), and then in the future, enhance your portfolio by building new bedrooms in basements and attics?

Then an other extremely interesting question...Click on the horizontal 3 green dotties..Apparently you can ignore users.What happens if I ignore myself?...

Just a side note when doing signs make sure you use horizontal signs (the tubes run horizontal as oppose to vertical) to hang on the post as they are less likely to bend from the wind.You can drive for dollars, you can use flyers or door hangers and go door to door.

When you take pics, take horizontal and make sure EVERY single light is on.

The basement, like the one you saw, had several inches of water in it due to a large horizontal crack in the block foundation wall about 2 feet off the floor.