[Pisces]

My trick for calculating range with the attackdisk backside:

1: lookup mastheight in meters in the recognition manual
2: measure centiradians in the periscope view. Try to gauge it down to a 6th centiradian. Remember which zoom level you use.
3: locate the mark on the inside scale of the (light yellow) distance disk which best represents the mastheight (28m, so 2800 in your example)
4: Locate the centi-radian value as a minute-mark on the time-disk. The centi-radian fraction is then equivalent to a multiple of the 10 second intermediate marks. 2.7 is just over 2+4/6, so also just over 2m40s.
5a: For low zoom, look over at the distance value against 10 minutes (this is equivalent to 1 minute): 28m/(2.666 centi-radians)= 10.5 (hundred meters)
5b: For high zoom, look over at the distance value against 4 minutes (4 times the 1 minute mark): 28m / 2.666 *4 = 42 hundred meters.

By using centi-radians as minutes on the time disk you get to see the distances for both zoom levels all at once. Much quicker than guesstimating and approximating with the in-game distance table.

[EDIT]: And for centi-radians below 2 you look to the beige/tan disk showing down into the minute and seconds. All second marks line up with the multiples of 10 seconds on the white minute scale.