By numeric, we mean that instead of using a formula to determine how m,T and z are related, we use a table of values. You're probably already familiar with this method. In the case of the chicken, let's suppose that the function f relates the mass and temperature to the cooking time according to the following table.
| oven | m (kg) | |||||
| temp (F) | 1 | 2 | 3 | 4 | 5 | 6 |
| 300 | 70 | 75 | 80 | 85 | 90 | 95 |
| 350 | 65 | 70 | 75 | 80 | 85 | 90 |
| 400 | 60 | 65 | 70 | 75 | 80 | 85 |
| 450 | 55 | 60 | 65 | 70 | 75 | 80 |
To use this table, simply choose values for the mass, m, and the oven temperature, T, then look up the time. For a 4 kg chicken at 350 degrees, we expect (from the table) that it will take 80 minutes to cook. Thus, f(4,350) = 80.