Unfortunately, this doesn't mean what you think it means. Haste provides a a linear scaling to the base, pre hasted, DPS of the spell, but AFAIK, the next +1% on DrDamage represent increases of 1% over the total current DPS of the spell.

Let's define some variables:
Ha: Current Haste Ratting Value
x: Increase in Ha that we want to see how it affects DPS (It's what Dr Damage should display in the tooltip)
vHa: Cast speed with total haste=Ha
vHa' Cast speed with total haste=Ha+x
t: Time
nHa: Number of spells cast over a period of t, with haste=Ha
nHa': Number of spells cast over a period of t, with haste=Ha+x
dps': DPS with haste=Ha+x
dps: DPS with haste=Ha

We assume that 100% haste-> 1577 haste ratting exactly, though the exact value can ge obtained with the api functions

I've found a bug with the amount of haste needed for an 1% increase. The addon always lists 15.8 on my warlock, even if I do have greater than zero haste. Haste works like crit in this respect, and that is, the more you have, the more you need for an 1% increase in damage.

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Unfortunately, this doesn't mean what you think it means. Haste provides a a linear scaling to the base, pre hasted, DPS of the spell, but AFAIK, the next +1% on DrDamage represent increases of 1% over the total current DPS of the spell.

Let's define some variables:

Ha: Current Haste Ratting Value

x: Increase in Ha that we want to see how it affects DPS (It's what Dr Damage should display in the tooltip)

vHa: Cast speed with total haste=Ha

vHa' Cast speed with total haste=Ha+x

t: Time

nHa: Number of spells cast over a period of t, with haste=Ha

nHa': Number of spells cast over a period of t, with haste=Ha+x

dps': DPS with haste=Ha+x

dps: DPS with haste=Ha

We assume that 100% haste-> 1577 haste ratting exactly, though the exact value can ge obtained with the api functions

Now, we wish to have an 1% increase, that is dps'=1.01*dps

Since we're interested in the effects of haste on DPS, and those efects are always relative to the current value of DPS, we can normalize by DPS

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The formula for haste is:

AmountOfHasteFor1%DamageDncrease=AmountOfHasteFor1%HasteIncrease+0.01*CurrentHasteRatting

I'll post the calculations that led me to this if needed