I agree with all other replies. But I am not sure anyone explained what this "3/4 scale deflection" means. As what you quote seem like limits, I will attempt to explain it in as easy a way as I can.
Talking about lateral distance... When your CDI/OBS/HSI is tuned to (and identified) a VOR station, you can see 5 dots on either side of the centreline of the instrument. Each dot represents 2 degrees. So if I am tracking the 240 degrees TO the VOR, then if my needle is on the second dot to the right of the centreline of the instrument, then that means that I am 4 degrees to the left of the desired track. (Hence I must turn right to regain track).
For you to understand the scale, full scale deflection whilst tracking a VOR means that I am 10 degrees or more off the desired track (as the instrument has 5 dots either side, each dot is 2 degrees hence 10 degrees [or more]). Half scale deflection means that I am 5 degrees off course (or 2.5 dots either side). Hence 3/4 scale deflection would be 7.5 degrees off course (or 3.75 dots either side).
I used the VOR because the scale remains constant, and it was an easy way to describe the term "scale deflection".
The term 3/4 scale deflection for VOR tracking means that at all times during your tracking, you must not stray more than 3.75 dots either side of the centreline. (meaning no more than 7.5 degrees off course)
Should you be doing an ILS, as explained above, the instrument abides by a cone, so the closer you get to the ILS beacon - the smaller the scale (hence the smaller the movement required to regain / lose track). This is true for both vertical guidance (glideslope) and lateral guidance (localiser).
So the term 3/4 scale deflection for an ILS means that at all times during the approach procedure, the needles must not exceed 3.75 dots (or 75% of the available space) on both lateral and vertical guidance needles.