1) Math in tcl requires the use of the
expr command enclosed in [ ] or " ".

2) GETVAL is required by the tcl
'keywords' (i.e. built-in tcl commands like expr) to get the value
of a WebAccess TAG.

The @ does not work with tcl 'keywords'
(i.e. built-in tcl commands like expr).The @ is a shortcut for
ACTION commands. If the command is in CAPITALS then @ will
work. If the command is lower-case, you must use [GETVAL
].

3) $ is required by the tcl 'keywords' to
return the value of a local script variable (e.g. a variable
created with the "set" command).

4) Tcl uses a syntax that interprets
spaces as end of a command unless a delimiter is used. A
delimiter can be curly brackets { }, square brackets [ ] or quotes
" ". The delimiters are evaluated differently.

Square brackets [ ] are usually used with
the expr command.

Curly Brackets { } are evaluated as
literal command with no substitution.

5) Trigonometric functions (sin, cos,
tan, etc.) use RADIANS as there output or expected input (not
degrees). To convert radians to degrees, multiply by 57.2957795
(which is 360 divided by 2 pi).