7.5 Charting Price changes of two stocks

To compare prices fo different stocks, we need to calculat the price change:

NS <- function(xdat) xdat / coredata(xdat)[1]
a <- NS(Cl(AAPL))-1
g <- NS(Cl(GOOG))-1
m <- NS(Cl(MSFT))-1
            subset = '2007',

addTA(g, on=1, col="red", lty="dotted")

addTA(m, on=1, col="blue", lty="dashed")

The option lty is to make the line becomes other line styles where dotted means dotted line and dashed means dashed line.