A normal cylindrical surface is one whose axis is perpedicular to one of the principal planes of projection. The axis of the cylindrical surface will show as a point and the surface itself will appear as a circular edge in that plane. In the other two views the cylindrical surface will appear as a rectangle. For a simple example consider a pop can, which is a simple positive cylinder. If you hold the can as if you were ready to drink it, the axis of that cylinder will appear as a point, and the cylindrical surface appears as an edge. In this case the cylindrical surface is perpendicular to a projection plane placed between you and the can. If you then leave the can in that position and view it 90 degrees from the side, the can would appear as a rectangle, and if you view it directly from the top it would also appear as a rectangle. In each of those two views the axis would appear true length (TL).