$maxof

Returns the larger of a pair of numbers.

$maxof(number1,number2)

number1	a number or an expression that evaluates to a number
number2	a number or an expression that evaluates to a number

The value returned by $maxof has the same number of decimal places as the number that is returned.

The function returns the larger of a pair of numbers.

if event.eventname = "up"
let IndexPtr = $maxof(IndexPtr-1, 1)
else
... other commands ...
endif

Modifies an array index, without letting the index drop below 1.