Mike Welsh, director of Digital Signage for AccuWeather, Inc., said there are two kinds of signs that people typically see displaying temperature readings and time of day.

The older version, an LED sign, may have its own clock and sensor built in. The newer style is more like a TV monitor.

IT specialist Tom Kerley Jr. of Kerley Signs in Washington, D.C., said these full digital boards can get their content, including weather, from a subscription service.

What that means is, with a newer sign, the temperature reading may not be accurate to that exact location.

The temperature may very well be correct - for an authorized airport thermometer that happens to be miles away and provides the generic reading for the entire zip code.

Also, that information may have a time lag and can be affected by slow updating or Internet service interruptions. Either of these, Welsh said, "could cause content not to be as fresh."

Many airport observations only report once an hour, according to AccuWeather.com Senior Forensic Meteorologist Alex Sosnowski.

However, Kerley said that these fully digital systems that are fed information are less common because of the expense.

"Most of the time, it's always a temperature sensor on the sign," Kerley said.

According to Kerley getting an accurate reading, "depends on where you mount [the sensor]."

It is no surprise that a thermometer placed on a lawn, or worse, in a parking lot (where many bank thermometers reside) in the heat of the sun will register much higher than in a shaded area.

Watchfire Signs manufacturers the temperature gauges used by Kerley Signs.

It's not surprising that Joeff Koebrich, Watchfire's vice president of engineering, said the "big problem is how do you get the temperature right in the sun?"

His company makes the "Gill Shield" which is a type of guard for the thermometer.

Kerley described the sensors on the signs as a plastic "honeycomb."

"The temperature sensor is buried in the Gill Shield," Koebrich said, explaining that the shield shades the sensor and allows for a breeze that helps maintain the ambient temperature.

The sensor then sends a digital signal back to the sign.

To promote accuracy, Koebrich said the sensor takes a reading every minute then averages the temperature readings over every 10 minutes, reducing the chances for faulty readings to skew the temperatures seen by people on the street.

The National Weather Service collects its own official temperatures with thermometers and sensors that are shaded and positioned about 6 feet above the ground in a well-ventilated enclosure.

Sosnowski said reasonable temperatures can also be attained by simply locating a thermometer out of direct sunlight year round at a similar height.

He also cautioned that sensors should be kept away from things like dryer vents, which would produce temperature changing exhaust, or concrete, asphalt or other surfaces that would generate heat.

Keeping a temperature gauge above the ground helps avoid extreme temperatures and produces readings that are roughly accurate to what pedestrians are feeling.

When banks set up a new digital sign, or when you set up your own home weather system, location should always be taken into consideration. An extension cable for digital thermometers to allow for placement in a spot that will produce the most accurate readings.

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