Paul
That line checks for the value of a variable called vLastAlert (which needs to be global ie declared outside of the main function and initially set to for example 0) to be not equal to 1 and if the condition is true it draws a line at the prior bar relative to the one being currently processed. For an explanation of the various parameters of the drawLineRelative function see the related article in the EFS KnowledgeBase
If you are looking for examples on how to do this search the EFS forums as this topic has been covered at length before
Alex
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