If you purchased a home 20 years ago, its value today is likely triple your original purchase price.

It's also a good bet you have since refinanced your original 17 percent interest rate mortgage for one that costs half as much and you've tapped what could be hundreds of thousands of dollars in equity to send a kid to college, to take a long vacation, to refurbish the home or to move up to another home.

Ten years ago, if you indeed used your equity to move up to a new home, its value has now doubled, you are enjoying renewed equity returns and you now should be paying hundreds of dollars less a month with a refinanced mortgage several interest rate points cheaper than your original move-up mortgage with its 10 percent interest rate.

And, according to real estate investor Robert M. Campbell, determining when to make those moves over the past two decades should have been a no-brainer.

Consumers who watch the real estate market like investors watch the stock market can buy and sell homes with the acumen of a shrewd day trader, says Campbell, also a San Diego-based mortgage and real estate broker, who publishers the Web-based San Diego Real Estate Report.

It takes time, practice and patience and you won't make a killing over night, but over time you will enjoy the security of a roof over your head that doubles as an investment with hefty returns.

Regularly plotting a set of real estate market trends on a spreadsheet, reading the trades to watch the trends and investigating realty market ups and downs can help you determine the right time to buy or sell a home -- at a sizable profit -- says Campbell.

Campbell, who has an MBA in finance and another degree in economics, says his training and experience makes him better than the average number cruncher at interpreting trends' nuances and pinpointing moves. It's his experience he pitches when he markets his services to prospective clients who would rather he do the market analysis work.

"I know what's more important and what's less important, but that's what I do. That's my competitive advantage," he says.

He insists, however, consumers can also play the game -- and win. Because real estate market change occurs relatively slowly, consumers don't have to aim for a moving target, but can successfully shoot for the window of change.

"Every month follow a publication or publications to get the five key indicators. Start logging them. Use a spreadsheet to chart them. One or two months doesn't make a trend. Trends develop over the long term. Create a graph and start seeing them go up and down. This is not what I think. This is what the market tells me," Campbell says.

So what are those five key indicators? Cautioning that one indicator alone does not make a trend or a decision to buy or sell, Campbell says, in the order of significance, the key indicators to watch are: