Chart Time Scale Definition

The Chart Time Scale refers to the amount of time covered by each bar in a price chart. For example, here is a collection of three charts with different time scales for AAPL.

Weekly Chart

The bars on the weekly chart open with Monday’s opening price and close with Friday’s closing price.

Daily Chart

The bars on the daily chart open with each day’s opening price and close with that day’s closing price.   This is the most frequently shown chart time scale.

15 Minute Chart .Daily Chart

 On a 15-minute chart, each bar is 15 minutes wide. The first bar of the day opens with the market open at 9:30am and closes 15 minutes later at 9:45. The next bar opens at 9:45am and closes at 10:00am. This continues throughout the day with 26 bars showing the trading for the 6.5 hour regular session of each day.

Extra Insight:

Since I am using End-of-Day data for backtesting, the corresponding chart time scale is daily.

Different vendors calculate the weekly charts their own ways. TradeStation, shown above, always starts the week on Monday open and ends on Friday close. I believe this is the usual way of doing it. Telechart, however, closes the weekly bar as of the most recent close and uses the open from 5 days ago as the open of the weekly bar. So a weekly chart on a Wednesday in Telechart shows Thursday – Wednesday “weeks” for every bar on the chart all the way back.

Last updated 11/11/08.

Tags: backtesting, data, Telechart, TradeStation