A holographic data storage medium having an anti-reflective coating is described. The motion detection mechanism is magnetically coupled to a pointer rotation mechanism configured to indicate the position of the diaphragm and the corresponding pressure sensed by the diaphragm. The second axis is substantially perpendicular to the first axis, Each of the absorbent sheet products comprises at least one outer panel at least partially sandwiched between a pair of outer panels of an adjacent one of the absorbent sheet products of the stack. In a second mode, a maximum channel vector length is used, as retransmissions are less probable in good channels.