i fear i may have misrepresented the rd edition when i wrote note above i should have written superscript looks like or in gbooks' representation when i looked at this entry on p before it looked like also on explanation of table p i read the data in the table have many sources including both the primary literature and evaluated compilations the handbook of data on organic compounds third edition ref and the combined chemical dictionary ref were important sources other useful sources of physical property data on organic compounds are listed in refs the values in the table for the normal boiling point and the melting point that are accompanied with uncertainties in parenthesis have been critically evaluated using the nist thermodata engine tde ref designed to implement the dynamic data evaluation concept refs this concept requires large electronic databases capable of storing essentially all relevant data known to date with detailed descriptions of metadata and uncertainties the combination of these electronic databases with expert system software designed to automatically generate recommended property values based on available experimental and predicted data leads to the ability to produce critically evaluated data dynamically 'to order ' the uncertainties listed are combined expanded uncertainties level of confidence approximately representing the most comprehensive measure of the overall data reliability refs so this suggests that some temperature values in the table are automatically derived but as i say the or is a raised reduced sized font not parenthesized so the superscript may well refer to alternate sample pressure i can't find whatever it references i apologize if this dwells on this source too much i think the consensus here that the bp is significantly higher than 'c is dispositive