OK I have just completed some testing as I thought something was amiss with the TBT and Attack periscope Graticules (Observation scope is probably affected as well but I didnt test.
Can someone else verify my tests.?
I made a simple mission with my S class perpendicular to a Kongo Battleship and a small old tanker.
Both ships were stationary throughout test.
I varied the distance to get accurate full Graticule distances rather than partial marks as it makes things more accurate.
I used the Kongo and this tanker because they represent both rather tall and short masts
IE: 42M for Kongo and 19.7M for tanker.
The Game manual states
Periscope on high range is 0.25 Deg for small graticule marks and 1 Deg for Large.
TBT is 0.2 Deg for small and 1 Deg for large graticule marks.
BTW: Its impossible to have 0.2 Deg for small Graticule markers on the TBT if the main markers are 1 Deg as there is only 4 spacings not 5 between large marks.
Here is my results :
Attack periscope: Small graticule spacings = 0.29 Deg
Attack periscope: Large graticule spacings = 1.16 Deg
TBT : Small graticule spacings = 0.16 Deg
TBT : Large graticule spacings = 0.64 Deg
In other words there is an error 0.04 Deg per graticle marker on both instruments, one larger the other smaller.
The error compounds if you were tracking on the surface with the TBT and then use the attack periscope for the final measurements.
The error may not sound like much but consider a Kongo at 1000M range useing the attack periscope.
Mast = 42M
Angle = 2.4 DEG
On your 0.25 Deg per graticule attack scope you see this as 9.6 markers.
Calculate 9.6*0.25 Deg = 2.4 Deg
Range to target = 1002 Meters.
But as we know the Markers are REALLY 0.29 Deg so 9.6*0.29 = 2.8 Deg.
An arror of 0.4 Deg or a more importantly a range calculation of 859 Meters.
A difference of 141 Meters or approx 60% the length of the Kongo Target.
A MK10 Torpedo travelling at 36Knots would take 8 Seconds to get 141 Meters.
Or alternately a Kongo can move 82 Meters in 8 Seconds at 20 Knots.