Impact Coefficient and Average Effective Mass
The impact coefficient – ICO is the ratio between the effective mass of the ball and the average impact mass (AIM) of the specific area on the racket string bed at contact. It reflects how fast we can swing the racket, while providing adequate control and energy transfer to the ball, despite not hitting the ball right in the sweet spot. In other terms, it means we can swing the racket faster, while still taking less risk of losing control and power because the impact point was away from the optimal point of contact. ICO is defined in the same area as AIM:
ICO is simply a ratio between the Average Impact Mass of the hitting area (racket) and the effective mass of the ball:
\(ICO = \dfrac{AIM}{m_{e,b}} = \dfrac{m_{e,r}}{m_{e,b}}\)
I made a good approximation fpr ICO calculations in the Customization tools Excel file, which you can get by subscribing to my Customization Tools. For more tech-savvy people, I wrote a Python code, to simulate the Effective mass more accurately. You can get it here on GitHub.
