10 per cent valley definition: Value of (m/z)/Δ(m/z) measured for two peaks of equal height in a mass spectrum at m/z and m/z ± Δ(m/z) that are separated by a valley which at its lowest point is 10 % of the height of either peak. For peaks of similar height separated by a valley, let the height of the valley at its lowest point be 10 % of the lower peak. Then the resolution (10 % valley definition) is (m/z)/Δ(m/z) and should be given for a number of values of m/z