A multi-tap key is one that cycles through multiple functions when you press it. Press " to stop multi-tap.
For example, the X key contains the trigonometry functions sin and sin/ as well as the hyperbolic functions sinh and sinh/. Press the key repeatedly to display the function that you want to enter.
Multi-tap keys include z, X, Y, Z, C, D, H, and g. Applicable sections of this guidebook describe how to use the keys.