Texas Instruments TITANIUM TI-89 - Manual (Page 284)

Constants and Measurement Units 284
If you want to convert to a unit other than the default, use the 4 conversion operator.
To convert 4 light years to kilometers:
4_ltyr 4 _km
To convert 186000 miles/second to
kilometers/hour:
186000_mi/_s 4 _km/_hr
expression_unit1 4 _unit2
For 4 , press
2 4
.