Multitasking typically requires people to make performance trade-offs: paying more attention to one task can improve performance there, but might lead to performance decrements on other unattended tasks. In our work we try to gain a better understanding of how people make such trade-offs. One difficulty in this effort is that performance is typically expressed in different units across tasks (e.g., “accuracy” of keeping a car inside a lane and “speed” of performing a secondary task such as dialing). How do people trade-off these different units?