Why using heated-top or add mineral oil in PCR - (Jan/02/2008 )

Still do not get the reason to use heated-top or add mineral oil if without heated-top. I went through internet information. Still very confused!
Many thanks

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Heated top prevents condensation that accumulate on the interior cap, thus prevents changing of the buffer concentration. MO covers the liquid layer thus does the similar job.

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Using heated top or mineral oil prevents loss of liquid. Changes in salt and buffer composition due to evaporation and condensation, might affect enzyme activity.

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