The unique balanced measurement method used in the Gemini permits small amounts of surface area to
be measured with nitrogen gas that otherwise would be measurable only with krypton. Low surface area
samples often displace many times more nitrogen than they adsorb, especially if composed of low-density
materials of large particle size. The standard, built-in, helium free-space difference measurement and
mathematical compensation routine typically can remove the effects of more than 99% of this sample
displacement, but the small amount remaining uncompensated can still be significant.
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