Short term instability possible mistake What is known specifically about the IPK is that it exhibits a short term instability of about 30 g over a period of about a month in its after cleaned mass 18 from what I think is the BIPM s source for this it seems to be more like 4 g over a period of about four months for the IPK figure 14 in that document The proceedings linked in footnote 18 give no source for the much higher value