HP 40gs User Manual page 104

Not enough data
If you are using the general
input form, you need to
specify at least three values
for the Triangle Solver to
be able to calculate the
remaining attributes of the
triangle. If you specify less than three, Not enough
data appears on the screen.
If you are using the simplified input form (for a right-
angled triangle), you must specify at least two values.
In addition, you cannot specify only angles and no
lengths.