This kind of question really makes me smile... and makes me happy I was learning how to do this sort of thing long before personal computers came along or anything even remotely called AutoCAD.

Here's how to think of contours:  they are points of equal elevation or the shoreline of water risen to that level.  And when you look at contours it's helpful to think of water in another way:  which way would it travel if it were a raindrop.

The answer in the second case is that a raindrop will always move the shortest distance or perpendicular to contour lines.  So the way to interpolate between contours is to draw a line between them that is mostly perpendicular to each.  Then you simply measure the length of that line and do the math to determine how to subdivide the distance.  If all you want to do is find an elevation half way between two contour lines you only need to look for a point halfway between them.

It's not rocket science.

Dave.

AutoCAD isn't built to do that sort of thing.  You might be able to write some kind of complex LISP routine to do it, but if you're going to work with contours, or more specifically digital terrain surfaces, you're going to need to use something like Civil 3D.

Dave.

If your'e using Civil 3d (even the older version) and have (or can create) surfaces, the process is conceptually simple. But it can be cumbersome to carry out (as you should expect with just about any advanced Civil 3D function). Are you using Civil 3D?

Or now I'm wondering whether I misunderstood.  If you want to pick a single point, which won't necessarily be halfway between two contours in the XY direction, and you want the elevation at the same proportion of the distance in the Z direction as the point is between the two contours in the XY direction, that can certainly be done, but it's more complicated.  A routine would need to "reach out" somehow to find the adjacent contours, such as possibly with increasingly larger crossing windows until it finds two, and do some calculations based on the nearest points on them.  Does that sound like what you're after?

thanks, You are using Code to explain my Query. Please Elaborate it.