How accurate are old weather records, say from 100 years ago?

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Dear Tom,
How accurate are old weather records, say from 100 years ago? Pretty bad, I assume.
Peter Warren, Naperville
Dear Peter,
Weather records taken 100 years ago, or longer than that, were very accurate, and in some respects were more reliable than those taken today. Weather Bureau thermometers in the early 1900s were accurate to 0.1 degree and dew point temperatures were hand-calculated using ventilated wet-bulb readings. Today’s electronic temperature sensors are considered accurate with a tolerance of plus or minus two degrees and automated dew points are given a tolerance of plus or minus four degrees. Precipitation was measured using accurate 8-inch rain gauges, whereas today’s automated systems employ a less reliable tipping bucket rain gauge that tends to give faulty readings in times of high winds and episodes of heavy frozen precipitation.

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