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+ 5cm speed
- 1DC
First strike
Inspiring (normally +50 pts?)
+1 DC
Disrupt
Slowfiring (can build into spreadsheet by halving firepower)
Inv Save
Jumppack (small movement bonus -10pts?)
Sniper
Carapace hive (choose price and playtest)
Ignore cover (I\'ll incluse guardsmen in cover as one of the test groups for firepower)
leader (normally 25pts?)
Indirect fire (worthless? titan weapons here have max range of 60cm, and titan height makes direct fire normally easy)
Some of these are quantifiable. DC, movement and armor are pretty easy to factor into overall calculations. Again, though, they will vary by chassis. Some of the other factors can be ballparked based on some hand-waving kinds of comparisons. For example, we know Ignore Cover will be a substantial boost in firepower against a pretty specific but not uncommon kind of target, so you figure out the likely proportional increase in firepower based on that.
Use the square root rule for your math-hammer:
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Square Root Rule - the Square Root Rule is an axiom of military planning that says that doubling the firepower of a unit does not double the effectiveness of a unit because the same amount of damage can still take it out of commission. It improves the unit by roughly the square root of 2. The reverse is true for making something twice as tough - it only puts the same amount of fire downrange. In order for it to be twice as effective, it would need to be twice as shooty and twice as tough.
This has obvious implications for point-based systems and if you examine units in established armies, you will find they stick pretty closely to this kind of formula.
That's pretty obvious for DC.
Same for Invulnerable - just factor it into overall armor saves.
For firepower, I generally consider ranged firepower and assault firepower as separate factors in terms of calculating multipliers.
Assault firepower is mostly based on FF, with 1/3 or less coming from CC.
For speed increases, I generally use a square-square root rule. While it is important, it's definitely less so than raw firepower and durability.
For a lot of the less quantifiable values, I tend to simply round. For example, I would factor Jump Packs in by rounding up at some point in the calculations when I might not otherwise.
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So, to give an example, if you give a Warlord titan an upgrade that makes it 5cm faster, but cuts it -1DC...
-1 DC is a 1/8 cut in overall damage it can take and how many BMs will break it, or .875x as tough. There are some other considerations like the void shields staying the same and potential critical hits which negate lots of DC, but this will be close enough.
+5cm move is 1.33x the starting 15cm. I normally take a square root of a square root for movement, so that's where I'll start. However, experience has shown that increasing speed for a slow, very tough unit like this tends to be quite effective. If it comes down to it, I'll definitely use this as a factor for rounding up estimated point comparison.
SQRT(.875)*SQRT(SQRT(1.33)) = .935*1.07 = 1.00 cost multipler
So, basically, -1DC, +5cm speed is about a wash for a Warlord. Testing might show it to be different, but that should be a solid place to begin. You might consider rounding it up to +25 due to historical effects of adding speed to big WEs, but I think 0 is okay due to the next comparison.
We can do a quick cross-check to see how that fares with other comparable units. Compared to a Reaver chassis, it would be the same speed, +1DC, with an extra weapon system. DC and weapons are factors of 1.167 and 1.333, respectively
SQRT(1.167)*SQRT(1.333)*650 = 810 points.
That's a touch lower than starting from the Warlord basis, but it's just a rough cross-check and we didn't get into things like the Warlord having better CC. I think it shows that an even swap is about right and the potential +25 rounding up mentioned above is not needed.
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For a Reaver, the proportional decrease in DC is higher and the proportional gain in speed is considerably lower. You'd end up with...
SQRT(.833)*SQRT(SQRT(1.25)) = .91*1.06 = .965 cost multipler
.965 * 650 = 627.4 = 22.6 point decrease
So, it went from being roughly flat on the Warlord to a decrease on the Reaver. I'd round this to the obvious -25 points and test from there.