Subtract two aggregates from two different tables(two different datasets)

Migrateduser

<p>Hi forum,</p>
<p>I am currently designing a report in eclipse(birt,Eclipse BIRT Designer Version 4.4.2.v201410272105) but i am faced with a challenge, I have two tables in a grid and i need to subtract their totals from one another, I have tried global variables but they do not seem to work in the onCreate script of my aggregate.</p>
<p>I have tried checking other forums for similar issues but I cannot seem to find a solution, any help will be greatly appreciated.</p>
<p> </p>
<p>Kind Regards</p>
<p>Louis</p>