Editing Warhammer 40,000/8th Edition Tactics (section)

====Penetrating Saves====
Basic saving throws work very intuitively, broadly identical to accuracy a 6+ save works just like 6+ to hit - except that the target assigns which model takes the save in the unit and rolls the saving throw, this changes the looks of the math a little since we will be calculating how likely we are to penetrate our opponent's save rather than how likely we are to save. Many weapons have a negative AP value that increases the dice roll your opponent needs to beat to pass their saves, a cover save now adds a +1 modifier to the Sv of the unit rather than providing an alternate save like an invulnerable save like it did in the past. A saving throw roll of 1 is always a failure, but a roll of 6 is not necessarily a success. Invulnerable saves are unaffected by cover and AP but otherwise works exactly the same way as a normal save.

Your odds of penetrating (oop) is (Sv - modifiers - (AP) - 1) / 6 

*Note that oop cannot be greater than 6/6.
*Note that since AP is negative (-1/-2...) the outcome of AP is actually positive -(-1)=+1. 
*An ability to re-roll will multiply this value by (36 * oop - x * (7 + Sv + modifiers + AP) ) / 36 * (oop) where x is the number of facings on a saving throw your opponent can re-roll, so if your opponent re-rolls 1s x is 1, re-roll 1s, 2s, 3s and 4s x is 4.
*Ap increases damage non-linearly, having AP- or AP-1 against a 2+ Sv and a 6+ Sv are very different things, against a 2+ Sv AP- will need 6 wounds to penetrate the save once, while AP-1 will need 3 wounds to penetrate the save once (causing 100% more damage), while against a 6+ Sv AP- will need 1,167 wounds to penetrate the save once, while AP-1 will need 1 wound to penetrate the save once (causing 16,7% more damage).
 
=====Cover=====
Cover improves the Sv of the unit that is in cover by 1 against Shooting attacks regardless of which phase that Shooting attack is made in or whether the target or firing unit is in combat. A model cannot claim multiple cover saves, it is either in cover and receives the bonus or it is not and it does not benefit. If you have a unit that is partially eligible for cover the whole unit will not benefit, but if you remove all the models from the unit that are not eligible the unit benefits immediately, therefore it can be beneficial to roll your saves one at a time and pick off the ones outside cover first. 

*Certain units and terrain types (in the advanced terrain rules) have special rules which require additional restrictions regarding what units count as in cover or not. The best way to negate this if you want to maximize your output is to spread Anti-Armour units out across the board for as many viewpoints as possible. As for actually using this type of cover yourself, your best bet is to park these units inside a building or in a covered corner of the board where the opponent can't try to maneuver into a better place to shoot.
**Most TITANIC units require you to have them '''''in''''' cover '''''and''''' be 50% or more obstructed from view from the shooter (and sometimes this simply doesn't apply to some models). This would found as a special rule of the TITANIC unit itself and is not, strictly speaking, a rule for all TITANIC models. 
**Woods require non-INFANTRY units to be '''''in''''' cover '''''and''''' be 50% or more obstructed from view from the shooter.
**Ruins require non-INFANTRY units to be '''''in''''' cover '''''and''''' be 50% or more obstructed from view from the shooter.
**Craters only provide cover to INFANTRY.
**Barricades require INFANTRY units to be within 1" and behind it from view from the shooter. They do not provide cover to non-infantry.
**Obstacles do not provide cover.
**Imperial Statuary provides cover to MODELS that are within 3" and 25% obscured from the point of view of the firer.
**Fuel Pipes require INFANTRY units to be within 1" and behind it from view from the shooter.  They do not provide cover to non-infantry.
**Battlescapes require non-INFANTRY units to be '''''in''''' cover '''''and''''' be 50% or more obstructed from view from the shooter.
**Hills do not provide cover.
*A special note that terrain obscuring requirements from the view of the shooter doesn't have to be obscured by the terrain feature itself. A Vehicle could be on a Battlescape terrain feature which did not conceal them, but if another terrain feature or model obscured at attacker's view of them, it would meet the requirement to be obscured from the view of the firer.
*Many of the terrain types have additional special rules, but not rules related to meeting the requirements for cover saves.