Texas Instruments TI-73 Software Manual page 11

Subtraction
Example: 56 29 = ?
First, the value 56 is regrouped into 4 tens and16
ones. Now, 9 can be subtracted from 16, leaving 7 in
the ones column.
Next, 2 tens are subtracted from 4 tens to arrive at the
final answer of 27.
TI-73 / TI-83 Plus Math by Hand Application Page 11