Getting "nan" is the history data table from the Chart Builder.
22-Jan-12 12:45:06 AM CST 85.1 °F nan °F
22-Jan-12 1:00:06 AM CST 86.1 °F nan °F
22-Jan-12 1:15:06 AM CST 86.0 °F nan °F
TAC I/A Series
IA Series G3 (niagara)
The history table data is displayed in the table with the date and time stamp and then the data for the individual objects being compared in the chart builder. The time is displayed in HH:MM:SS format however the actual sample time has a millisecond component as well. If the time stamps for each object don't match exactly (including the millisecond value) the actual values for the objects that don't match will be displayed as "nan".
The way to make the History table data show values for each object for every timestamp is to change the "rollup" to something other than none. If you change the rollup to match the sample time in the history data the report will look best.