Strange broadcasting results

F = 59411.4
n = 12
K = [220.0, 900.0]

@show S_1 = F/(n*K[1])
@show S_2 = F/(n*K[2])
@show S_dot = F./(K.*n)
@show S_nodot = F/(n*K)
@. S_atdot = F/(K*n)
# S_alldots .= F./(K.*n)  # UndefVarError: S_alldots not defined

produces:

S_1 = F / (n * K[1]) = 22.50431818181818
S_2 = F / (n * K[2]) = 5.501055555555555
S_dot = F ./ (K .* n) = [22.50431818181818, 5.501055555555555]
S_nodot = F / (n * K) = [1.2688828052190122 5.190884203168686]
ERROR: LoadError: UndefVarError: S_atdot not defined
Stacktrace:
 [1] top-level scope at /Volumes/home/AD2000/Smin_not_defined.jl:10
in expression starting at /Volumes/home/AD2000/Smin_not_defined.jl:10

What is being calculated in S_nodot?
Why @. produces error here, and what does it mean "S_atdot not defined" as S_atdot stands on the left side of the expression?

Julia 1.3.0 on Win10 and 1.3.1 on Mac 10.14.6

F * pinv(n*K). See @edit F/(n*K).

Here it means “assign to elements of S_atdot after calculating the result elementwise”, so it has to exist. Perhaps you meant

S_atdot = @. F/(K*n)

See the manual on broadcasting.