What was once a need for monthly data became a need for daily and even hourly readings of the meters.

For example, he said, a computer-based continuous radon gas monitor test would produce hourly readings over an extended time.

The true daily mean, obtained from a thermograph, is approximated by the mean of 24 hourly readings (which is not the same as the mean of the daily minimum and maximum readings).

For days, Beijing has been trapped under a blanket of yellow-brown murk that the U.S. Embassy air monitor classifies, in its hourly reading, as "hazardous."

Doc's played it safe and taken hourly readings for a while.

Active radon testing devices require power to function and usually provide hourly readings and an average result for the test period.

"The final environmental impact statement should include a detailed plan for air and sound monitoring around the periphery of the site during construction, with the hourly readings posted," Ms. Martin said.

The average temperature for this July - counting hourly readings around the clock - has been close to 81 degrees, 4 above normal.

The mean sea level data was calculated from hourly readings of the sea level between 1 May 1915 and 30 April 1921.

The $5,000 electronic gauge records instantaneous changes in temperatures and keeps track of its own observations, unlike a mercury thermometer, which needs an attendant to take hourly readings.