For flights outside your local area, you will not often have the convenience of a plotted Skew T or, in many cases, even an upper wind report. Comparison of the winds between standard constant pressure chart surfaces will result in a vertical shear value, but this value can be lower than may actually exist, because of averaging. Considering that you are evaluating layers 4,000 to 8,000 feet thick between standard constant pressure surfaces, a layer of turbulence may be easily hidden. If your calculation yields a shear value indicating turbulence may be present, say 8 knots per 1,000 feet (or moderate turbulence), then you can be certain that you have a layer of at least moderate turbulence, possibly greater, somewhere within the thick layer you have just evaluated.