Every weekday morning, Kathleen Clover climbs up on the roof of a nine-story office building at 916 19th St. NW and retrieves a tiny glass square smeared with colorless goop.

She carries the slide down to her office, stains it with a few drops of pink dye, puts it under a microscope and starts counting dots.

The result is Washington's daily pollen count, reported by the D.C. Medical Society, the D.C. Lung Association and the news media.

Technically, the count represents the number of pollen grains that have landed on a one-square-centimeter glass slide during the previous 24 hours. Less technically, for people with hay fever, it represents a rough index of misery.

On Monday the pollen count reached 210, the highest so far this year. The high count was due to dry, windy conditions and a heavy dose of tree pollen, particularly from oaks, said Clover, who is a nurse.

"It's a very rough indicator," says Clover's boss, Dr. Yuill Black, an allergist who began reporting pollen counts here nearly 20 years ago.

Anytime the count exceeds 20, Black says, a fair number of pollen-sensitive people will get allergy symptoms. A count of 100 or more almost guarantees trouble for people with hay fever.

The highest count last year was 226, on May 3, during tree pollen season.

Black readily acknowledges the pollen count's limitations. It's an estimate, not an exact count. It doesn't distinguish among individual plants or trees; someone allergic to late-summer ragweed may not be affected by a high count due to springtime tree pollen. And since this morning's count measures pollen collected during the past 24 hours, it won't necessarily predict today's conditions.

But despite all those drawbacks, watching for changes in the pollen count can be useful to a person with hay fever.

"Pollen sufferers know that outdoors is worse than indoors," Black says. "If the count is high, they can postpone their jogging or their golf game and go to the movies."