Exploit the expansion and contraction of organic materials with changes in humidity; changes are amplified through the use of levers that move a needle or pointer.
•hair, catgut, goldbeater’s skin, textile, or plastichorse hair, human
-20 90% best range -Uncertainty from +/-5% up to +/-15% -calibrated with a wet rag to 100%; no dry end calibration -considerable hysteresis -responds to changes in humidity very slowly
+simple & fundamental measurement +relatively cheap ($35 to $80 for sling) +can have good stability +tolerates condensation without damage
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+precise measurement (+/-.1C) +wide measurement range (-100..+100C) +very good long term performance fundamental measurement +
expensive
--usually requires some skill/training to operate -mirror cannot tell ice or dew -contamination on mirror causes errors -requires frequent maintenance -complex in construction