1. **Problem:** Estimate $\tan 73^\circ$ to the nearest thousandth using a calculator. 2. **Formula:** The tangent of an angle in a right triangle is the ratio of the opposite side to the adjacent side: $$\tan \theta = \frac{\text{opposite}}{\text{adjacent}}$$ 3. **Calculation:** Using a calculator, find $$\tan 73^\circ$$. 4. **Result:** $$\tan 73^\circ \approx 3.273$$ (rounded to the nearest thousandth). **Final answer:** $\boxed{3.273}$