The benefits of the units system in the HP 48/49/50 series really cannot be overstated. You don't just get free conversions between compatible unit types, you a

The benefits of the units system in the HP 48/49/50 series really cannot be overstated. You don't just get free conversions between compatible unit types, you also get realtime type checking to prevent invalid operations on quantities with incompatible units. This eliminates a very common source of errors, and also encourages more rigorous labeling of quantities with units when you're working on paper. The TI-89 technically can also compute using quantities tagged with unit information, but the UI for it is too convoluted to be useful.