That should be "four degrees Centigrade".
To paraphrase Wikipedia: "The gram ... was provisionally defined in 1795 as the mass of one cubic centimetre of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the International Prototype Kilogram (IPK) was derived in 1875, had a mass equal to the mass of 1 [litre] of water under atmospheric pressure and at the temperature of its maximum density, which is approximately 4 °C."
The italics are mine.
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