Slide Rule Calculations

[Markus Witt]

Originally Posted by skip

First a big thanks for making this guide

Just received my slide rule would have liked it a bit bigger, guess my old eyes cant cope so well these days.

Anyways in your range finding tutorial I have a query

I have the hairline set to 2.62 on the D scale
When I move the 1 on the C scale to line up with 1.9 on the D scale I can read under the hairline 1.39 (1390m) on the D scale.. All good

however you said when in periscope zoom to move the 4 mark on the C scale and line that up with the 1.9 on the D scale, when I do that I read 5.55 under the red hairline.

I assume that the 19mrads eg only applies to the x1 scope and in the 4x scope you would get a different mrad value which you would use with the 4 on the C scale.

Cheers

Normally the scope is at 1.5x zoom and when zoomed in it is at 6x zoom, which is 4 times larger (6 / 1.5 = 4). This means that all objects you look at become 4 x larger but the scale of the graticules doesn't change.
So in our example the target with an angular height of 19 mrad would have an apparent angular height of 4 x 19 = 76 mrad when using 6x zoom. To find the range you still put the hairline over 26.2 on the D scale, but now you match 4 on the C scale with 76 on the D scale.
The range is still the same (1380m) and also note the 1 on the C scale is still pointing to 19 on the D scale. By the way, I think you put the hairline at 2.64 instead of 2.62, take another look.

[skip]

Thanks Markus

You were right enough I was using 2.64 rather than 2.62 on the D scale.

With regards to the periscope graticules you wouldn't happen to know which mods within SH3. SH4 and SH5 have the graticules set to the correct size and the value of the millirads at each zoom so that I can use the slide rule accurately. That would be a big help if you knew because after trying your examples with SH3 vanilla and SH3 greywolves expansion the periscope graticules don't appear to scaled properly as none of my calculations were working.

Other question with regards to finding a targets AOB how do read off values larger than 90 accurately on the slide rule ?

Again many thanks

[Markus Witt]

Originally Posted by skip

With regards to the periscope graticules you wouldn't happen to know which mods within SH3. SH4 and SH5 have the graticules set to the correct size and the value of the millirads at each zoom so that I can use the slide rule accurately. That would be a big help if you knew because after trying your examples with SH3 vanilla and SH3 greywolves expansion the periscope graticules don't appear to scaled properly as none of my calculations were working.

The scale of the graticules are fixed and designed for normal zoom (1.5x). If you increase the zoom to 6x objects appear 4 times larger but the scale of the graticules does not change. So when zoomed in the apparent angular height is 4 times larger than the actual angular height. When using the slide rule to find the range you can correct this in 2 ways. You can divide the apparent angular height by 4 to find the actual angular height and point the 1 on the C scale to this value. Or you can point the 4 on the C scale to the apparent angular height. The last method is easier and note that by matching the 4 to the apparent angular height you are in fact dividing it by 4.

Regarding SH3 and GWX I haven't played this in quite some time (I've only played SHV WoS the past few years) so I can't remember if the graticules in these games are actually measuring millirads. In SHV WoS the graticules do measure mrads and the method as decribed works.

Originally Posted by skip

Other question with regards to finding a targets AOB how do read off values larger than 90 accurately on the slide rule ?

To find the sine of angles larger than 90 degrees just remember that the sine of 95 is equal to the sine of 85, the sine of 100 is equal to the sine of 80 etc.

[skip]

Thanks again Markus

Cant believe I forgot that if my AoB calculation came to say 60 degree all I had to was deduct 180 to get the correct 120 degree value. I am definitely reaching my senior years.

With regards to SH3 the graticules are definitely not measuring millirads too bad.

Looking forward to your next entry really pleased I purchased this slide rule.

Cheers

[Elphaba]

Have you seen SubBuddy ? It has built in training videos and tutorials and might be of help.

[Dieselglock]

I know this is a fairly old post but is there anywhere to download the pictures that went with the slide rule explanation?

[Markus Witt]

Originally Posted by Dieselglock

I know this is a fairly old post but is there anywhere to download the pictures that went with the slide rule explanation?

Still had them on my harddrive. Added them again to the text. I had to delete them in the past as I exceeded the sites maximum attachment Mb limit.
This was before I knew I could create an album to add photos.