MACD, or Moving Average Convergence Divergence, is a common indicator used by traders to mark potential buy and sell points. It looks to me as though MACD can only be calculated once per day using the closing prices of a lot of previous days. But most charting software shows an MACD line that changes throughout the day. What data would go into an intraday MACD line and how would this data be used to calculate it?
The MACD is calculated on the period data you are looking at. So if you are looking at a weekly chart the MACD would be based on the weekly data, if you are looking at a daily chart it would be based on the daily data, and if you were looking at an intra-day chart (say a 15 minute chart) then the MACD would be based on the 15 minute data.
If you are looking at say a live daily chart both the price and any indicators would change throughout the day based on the last traded price. This is why the MACD and other indicators would change through the day, the last traded price is being taken as the close price for that period and is continually changing until the end of the trading day when the actual close for that period is set.