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The Accuracy collection, or how Stalin guides your Bias

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Wanderjar

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Current Feb/28/19

So here's the post about accuracy. most of this is in bits and pieces from other spots so I'm gathering it all here and adding some new info etc. Have at it!

A quick note on dispersion: after turning for 1 second you have reached max hull dispersion and will carry that value until the turn rate is decreased or stopped.
Lets knock the nerdy parts out first... 

The Math

There are three factors affecting overall dispersion. One due to moving traverse (affected by Smooth Ride and Vstab), one due to hull traverse (affected by Clutch for the worse, Vstab for the better), and one due to turret traverse (affected by Snap Shot and Vstab),

MATH!

ComputedDispersion = GunAccuracy * SQRT (1 + DispMovingTraverse^2 + DispHullTraverse^2 + DispTurretTraverse^2)

where:

GunAccuracy = ReportedGunDispersion

DispMovingTraverse = DispersionMoving*HullSpeed (kmh)

DispHullTraverse = DispersionHull*HullTraverseSpeed (Deg/s independent of turret movement)

DispTurretTraverse = DispersionTurret*TurretTraverseSpeed (deg/s independent of hull movement)

Then Smooth Ride skill seems to be better than Snap Shot in many cases and the benefits of both are minor at best and misleading/useless at worst.

now with formatting for easy viewing!
disp = Gun accy*sqrt(1+forward moving^2 + hull turning^2 + turret turn^2)
                   ^                        ^                                ^                         ^
              base value          SR skill                        nada                Snap skill    <-- skills that help. BIA and VStab helps all.


and the files you can verify it in is: 
res/scripts/avatar.pyc
it's unencrypted but you do need a tool reader to view it. Also the lang is python if its not obvious. Some people are reporting this as being encrypted. WG uses the Blowfish cipher, and its not too hard to break.

Accuracy and Dispersion

Gun Accuracy

The accuracy value for a gun is given in meters at a range of 100m. The lower the value the more accurate your gun is. The value describes 2 standard deviations σ from the center of your aim. In other words, for a gun with 0.32m dispersion at 100m, 95.45% of all shots will land within 0.32m of the center of your aim at that distance. Dispersion amount increases linearly with distance, i.e. 0.32m effective accuracy at 100m translates to 0.64m at 200m and 1.28m at 400m. 

Aiming Circle
Sigma Deviations
Standard_deviation_diagram.png (Picture sauce Thanks Mwtoews ) 

six_sigma_normal_distribution_2.jpg
WG uses a 2 Sigma system now (post 0.8.6) rather than the 3 sigma from before

The aiming circle (or reticle/thing that goes on the Red tanks...) describes the area of 2 standard deviations (2σ) from your aim point. Based on a standard normal distribution, this used to mean that 4.2% of your shots would fall outside of the aiming circle. Since version 0.8.6 (the sigma rework) any shots falling outside the 2 Sigma circle get a second roll with a flat distribution (pancake) to place them randomly within the circle (prior to this they were placed on the perimeter). Because of this the shots move (deviate) away from your aim point, outwards toward the edge of the circle, but never shoot past its edge. 

(the above partially shameless stolen referenced from the wiki. Thanks Haswell :D )

Equipment

Gun Laying Drive vs Vertical Stabilizer
Always always always Vert stab. 20% against ALL movement penalties. This means smaller bloom on turret moving, smaller bloom on hull rotation, smaller bloom on the move, Smaller chance of a miss overall. If you aren't running a Vert stab, it should be that you can't equip one. ALL scouts/lights can carry a Vstab now so there's no excuse.

LiS2R11.jpg Self explanatory chart

why start at 1.7x when you can start at 1.27x? It's a much tighter reticle and you still beat the GLD to minimum bloom by .3 sec? Obviously both are best but Rammer - Vstab - Optics are the Trifecta.

Vertical Stabilizer 
+20% to Accuracy during all Movement (AWSD) and Turret rotation

Gun Laying Drive 
10% faster aim in! Generally only useful for snipers and arty. To be used only if a Vstab isn't available AND you are planning to playing a non-peek-a-boom style. Generally not for heavies but sometimes, its what's there.

Vents
5% (3.7% effective) better everything, even general crew skills (but not job specific ones) 

FOOD! 
A Flat +10% (7.2% effective) to ALL Major Qualifications AND skills/Perks, a huge help in gun Handling and general tank performance

Skills

As long as you keep moving anything, the bloom continues to bloom, the skills and equipment help to counter the bloom growth. Vents, Vstab and BIA help to actively minimize the bloom dispersion values DURING turning and after as well, everything else just counters the bloom afterwards. 

BIA:  always useful, +5% to general crew skills and to major qualifications, but not to, say Recon or Snapshot) Requires ALL crew members to have it. It's a perk so its 100% effective only (also a good reason to train it 2nd or 3rd). The boost to the Gunner Qualification helps to minimize the bloom penalties by 2.5% effective.

Gunner
Snap Shot: Pretty useful for all tanks, even casemates and arty. Reduces bloom by 7.5% on turret rotation/Gun movement (3.5 effective). Works great with Vstab! Does stack with Driver's Smooth Ride skill

Driver:
Clutch braking: Tiny bit faster deg/sec PIVOT turning (A/D only, not W/S) than Off Road, but worse passibility all over. Good for casemates/arty and slow turning tanks (T67 hellcat, grille, T95 etc) 

This skill can affect Hull turn dispersion by making it worse/faster for a shorter period of time. Nothing makes it better save Vstab/BIA. Clutch Braking is still vital for tactical movement so it's validity isn't questioned but knowledge that it can make your dispersion worse while turning (A/D keys) should be paid attention to.

Hull traverse google doc: https://docs.google.com/spreadsheets/d/10VIumnYWrLsc2xpPFnZp-MaVdfBHg_xZOHb04ie1HU8/edit?usp=sharing  interesting if you want the raw numbers and why people are all Off Road > Clutch for non-casemates.

Smooth Ride: This skill is hotly debated. If your tank has more than .25-.27 dispersion on Forward movement (W key only), it's worth getting early. otherwise, its only use is to counter Clutch Braking's increased dispersion so you should train both this skill and Clutch at the same time to maintain current dispersion values. (more deg/s = more bloom) get if after ORD and Clutch. Look up your favorite tank at Tanks.gg in the stats or compare tabs! 


@8_Hussars and my work on SR/Snap/Clutch Dispersion values:
https://docs.google.com/spreadsheets/d/1TqvlcnQIdPpAzy3X0OK4lxdNjWoqo9ejcdRqu_HqIuc/edit?usp=sharing
.25 movement dispersion (which is fairly high) seems to be the 'useful' line for where SR is viable. save for sub tier 6 (and the scout/heavies of 6, not the meds generally) SR should be reserved for a 4th/5th skill. certain premium tanks (type 64, superP) benefit from having the skill but most won't see any kind of useful gain.

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