One way to compare regimens is to directly manipulate the parameters in the IMR calculator. You can work with any two of the three inter-related parameters: **total dose**, **# fractions**, and **Rx dose/fraction** by locking the parameter you wish to hold constant. Unlocked parameters have enabled editable text fields and "up/down" arrow bumpers. You can modify the parameters in predefined increments using the arrow bumpers, or enter exact values from the keyboard. The BED (E/α) is automatically updated when any of the parameters is changed.

For example, lets begin with a course of 30 fractions of 200 cGy. The total dose is 6000 cGy and the biologically effective dose is 72.00 Gy_{(10.0)}.

Now, lock the total dose field and change the new number of fractions to 25. The dose/fraction will change to 240 in order to maintain the locked total dose of 6000 cGy and the biologically effective dose readout will calculate 74.4 Gy_{(10.0)}.

Now, lock the number of fractions at 25 and reduce the dose/fraction field (to about 234 cGy) until the biologically effective dose returns to approximately 72 Gy