subtract element (n-1) from element n

I have a date/time wave and I want to create a new wave that has the difference between adjacent time points.  Is there a clever way to do this without an explicit loop?  Related to this, as always when I've been away from Igor for awhile, I've forgotten how to call a set of waves that have names that change each time through the loop.  See below.

do

	n=0

	string temp_string="degF_t"+num2str(i)

	string time_string="igor_time_t"+num2str(i)

	string time_string_temp="igor_time_t"+num2str(i)+"temp"

	Extract/O degF,$temp_string,thermistor==i

	Extract/O igor_time,$time_string,thermistor==i

	SetScale d 0, 0, "dat", $time_string

	duplicate $time_string $time_string_temp

	for(n=1;n<dimsize($time_string_temp,0);n+=1)	// Initialize variables;continue test

		$time_string_temp[0]==0

		$time_string_temp[n]=$time_string[n]-$time_string[n-1]			// Condition;update loop variables

	endfor						// Execute body code until continue test is FALSE

		$time_string_temp[n]= //??? want to set something so that on the final loop we do not have an index out of range error...

	i+=1

while(i-1<thermistor_max)