You can easily use HP48 to evaluate a function.
For example:
Lets evaluate the function y=sin(x)*cos(y)*ln(z)
for x=5, y=4 and z=3
1 - put y=sin(x)*cos(y)*ln(z) in level 1
2 - type { x 5, y 4, z 3} and press [ENTER]
3 - press
[SYMBOLIC] [NXT] [ | ] 4 - result:0.688604398373 ( with angle mode in radians)