"attempt to perform arithmetic on field '?' (a nil value)" Error help?

This is my function

function loop (frames)
    for i = 1,frames do
    whead.C0 = CFrame.Angles(math.rad(dh[1]/frames + h[1]),math.rad(dh[2]/frames +h[2]),math.rad(dh[3]/frames +h[3]))
end
end

loop(10)

I get this error on line 4 "attempt to perform arithmetic on field '?' (a nil value)" dh and h are tables with 3 number values( Hence the brackets [] ), frames is also a number value.

dh and h are originally 0 dh is the difference, h is the current rotation the empty dh and h are passed through a function giving it a value. But it they both start off as

h = {}
dh = {}
--then they go through this function which sets the variable in the table's value

function differences(new,current,difference)
    difference = new-current
end
--so it would be
differences(new**(which doesn't pertain to this problem)**,h[1],dh[] )