21.   Larry Taylor takes microscopic samples from the coating and measures levels of trace elements such as magnesium, iron and calcium.

22.   Later, Ferrando and NASA scientists will measure hormone levels and look for correlations and changes in each volunteer.

23.   Last November scientists went to the mountain, swept away snow and erected tents, placing instruments inside to measure gas levels.

24.   On the environment, the official added, one could measure the levels of persistent organic pollutants and whether loans made to reduce them were having an effect.

25.   Researchers used skin tests to pinpoint the proteins to which the children were allergic and measured the levels of different allergens in their homes.

26.   She and her colleagues are measuring the levels of dust mites, cockroach debris, cat dander, fungi, and other allergens in the homes.

27.   She and rangers from the National Park Service measured levels and studied the flow pattern of the exhaust, using smoke bombs to make the patterns visible.

28.   Some sample gatherers were told that the material was needed for a project to measure natural levels of the element radium found in the population, the documents disclosed.

29.   Students should be tested often to measure their level of academic achievement.