## Numerical Derivative

Press
to view the calculus menu, then
to select numerical differentiation, nDer.
The syntax is: `nDer( `

*expression*`,`

*variable*
[`,`

*value*]` )`

The numerical derivative option approximates the first derivative
of *expression* with respect to *variable* at *value*.
If *value* is omitted, the current value of *variable* is used.

**Note:** The value of the derivative is found by computing the slope of the line through
the points ( *value*- ,
f(*value*-) ) and
( *value*+ ,
f(*value*+) )
for some very small number .
The value of can be changed in the
tolerance editor available by pressing
.
typically has a value of about 0.0001.

Though this method is less accurate than der1, it can be used
to evaluate any expression, including a single nesting of itself for calculating the
second derivative.