Tips, tricks and frustrations: (From the big valley era):

1. Equations like t = 4 or inequalities like x < y get stored into variables
and not just their value. The string functions right() and left() doubles
as rhs() and lhs() functions.

2. Data/Lists/Matrix: It seems impossible to store into Data i-row j-column,
instead store into lists and then create the Data with the newData command.
Create and play with lists via makeList, then use makeData to combine the
lists.

3. Try to prevent yourself from using single-letter variables that are going
to be stored to. Someone might use s in a function, but s1 is not so likely.

4. Strange fact of life: You can't use q1 or q3 as a variable, but you can
use q, q2, q4 or q5. Go figure. (Well actually I did use q1 in a function,
I just couldn't store a value into it, nor read a value out of it.)

5. Ran out of memory for the 1st time on this project. 2nd Mem allows one
to trash stuff. (Just blindly reseted this time.)

6. Held a new ti-89 today, it is much less dense. (This is silly, mine has
the screen driver adding extra mass.)

7. DrwCtour function is faster and allows choice of the contours over the
old method of ncontours=1, and making contour_value = (zmin + zmax)/2.