To simplify the expression \( 9^9 \cdot 9^{-6} \), we can use the property of exponents that states \( a^m \cdot a^n = a^{m+n} \).
Applying this property:
\[ 9^9 \cdot 9^{-6} = 9^{9 + (-6)} = 9^{9 - 6} = 9^3 \]
Now we need to calculate \( 9^3 \):
\[ 9^3 = 9 \times 9 \times 9 \]
Calculating step-by-step:
- \( 9 \times 9 = 81 \)
- \( 81 \times 9 = 729 \)
Therefore, \( 9^3 = 729 \).
The numerical equivalent of \( 9^9 \cdot 9^{-6} \) is \(\boxed{729}\).