Is this 'Slow Monster probability' spoiler correct?

[Patashu]

GF_DO_SLOW with pow 20
if already slowed, the power is the new value it'd take on e.g. slow once, slowing more is much easier

resist_chance = r_ptr->level + 40 - (v / 2);

if (randint0(100) < resist_chance) return (TRUE);

uniques roll twice

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>>> for i in range (0, 71, 5):
... print "{0}: {1} chance, {2} for a unique".format(i, 1.0-(i+30.0)/100.0, (
(100.0-i-30.0)/100.0)**2)
...
0: 0.7 chance, 0.49 for a unique
5: 0.65 chance, 0.4225 for a unique
10: 0.6 chance, 0.36 for a unique
15: 0.55 chance, 0.3025 for a unique
20: 0.5 chance, 0.25 for a unique
25: 0.45 chance, 0.2025 for a unique
30: 0.4 chance, 0.16 for a unique
35: 0.35 chance, 0.1225 for a unique
40: 0.3 chance, 0.09 for a unique
45: 0.25 chance, 0.0625 for a unique
50: 0.2 chance, 0.04 for a unique
55: 0.15 chance, 0.0225 for a unique
60: 0.1 chance, 0.01 for a unique
65: 0.05 chance, 0.0025 for a unique
70: 0.0 chance, 0.0 for a unique

[Magnate]

It's a while since I looked at the mon-timed code, but that looks about right, yes.