Sentence:  In the structure of chrysotile 2"M"<sub>c1</sub> illustrated in Figure 7.6 is approximately 0.1 Å, and so overshift is 0.5 Å and the <WSD>undershift</WSD> is 0.3 Å, occurring in successive layers to produce a two-layer unit cell with B = 93.3°. 
Meaning of the word marked with <WSD> tags:  (mineralogy) The amount of displacement in the layers in a crystal lattice that places the layers too close together.