The first three boxes are velocity, in x y z.
The next box is the projectile type.
The next three are velocity variance, explained later, in x y z.
The last is projectile scale. Damage, explosion size, and projectile size are increased according to the scale.
About velocities.
If you set the first three to 0 0 20
Then the next three to 10 10 0.
It has a chance of shooting in -2.243 5.241 20, 7.001 -6.221 20, etc.
So anywhere between
x: -10 ~ 10
y: -10 ~ 10
z: 20 ~ 20
Where first three 5 6 10
and the next three 2 2 2
have this range:
x: 3 ~ 7
y: 4 ~ 8
z: 8 ~ 12
That's what Mr. Bill meant by the spread.