[amibroker] how to change negative price to positive in afl?

[rinku kumar <boyrinku@xxxxxxxxxxx>]

Hello everybody
tell me how can i change value to positive in afl if it comes in negative?
example
difference=(close-open);

if close is 100 and open is 90 then difference would be 10 and if open 
is 100 and close is 90
then difference would be -10
in result i just want difference between open and close so in both cases 
it should be 10
please tell me how can i do it?
thank you



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