How is decibels measured? Noise in general

Hi,
Looking at the products page for a ThinkPad T61 it says that the noise level is 36db. Do anyone knows how and where this level is measured? And are we talking peak or average level? I need to compare it with other laptops before purchase...
From the thinkpad owners: Is it true that a Thinkpad is one one the most silent (yet "high" performance) laptops in the market?
Thanks.

sorry typo I hope the bankers don't rob us all this year

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