Here is an example for shifting negative price history to the positive range. You must do that before loading the asset, otherwise it has only effect trading and live prioces, but not on historical prices.

Code
function run()
{
	set(PLOTNOW);
	BarPeriod = 1440;
	NumYears = 20;
	assetAdd("ZMeod");
	Detrend = NOPRICE;
	PriceOffset = 1000;
	asset("ZMeod");
}