hi
you need to add 2 triggers
Add trigger with 2 variable actions (not conditions)
action
set user variable 
name   num1
value   0
Add action
set user variable
name   lt1
value   0
no conditions
set trigger to favourite
set trigger to   one time only
Add trigger with 2 variable actions (not conditions)
so Add trigger
action
set user variable
name  num1
value  IF(s_1_last_traded>lt1,num1+1,IF(s_1_last_traded<lt1,num1-1,num1))
Add action
set user variable
name  lt1
value  s_1_last_traded
no conditions
set trigger to favourite
set trigger to no more than .30
the num1 and lt1 starts at 0 each new market
then the num1 is updated if the last traded is more or less than the last recorded last traded.
lt1 then records the new last traded value for the first selection,index 1
the s_1_ = index 1
so you need to do this for all the selections that you want to record the last traded price.
all you do is add a new action to each of the 2 triggers
num1 = first favourite
num2 = second favourite
and so on
lt1 = first favourite
lt2 = second favourite
and so on
remember to alter each s_1_last_traded
so for the second favourite it is  s_2_last_traded
and so on
if you need more help, then say the maximum selections that you want to record the prices for.
mcbee