a) Use an encoder
a1) Use a 'real' encoder
a2) Make one perforating the disk or with a reflexive optocopler counting the lines

b) Get the display control lines and De-decode from 7 segments to BCD

gud bai*

*The spansh writing of the sound 'good bye' ;-D

Apointing the Erik's wiew about SMS in my language 4 is 'cuatro' not 'for' so is difficult for me reading SMS style.

Regards.