A system comprising: a first building system (65, 67, 69, 71, 73) including a first sensor (100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 111) that generates first operating data corresponding to the first building system (65, 67, 69, 71, 73), the first operating data including a plurality of first data values generated by the first sensor and corresponding time values associated with each of the first data values; a second building system (65, 67, 69, 71, 73) including a second sensor (100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 111) that generates second operating data corresponding to the second building system (65, 67, 69, 71, 73), the second operating data including a plurality of second data values generated by the second sensor and corresponding time values associated with each of the second data values; a data server that receives and stores the first operating data and the second operating data over time; a user terminal (168. 169, 170) that accesses the first operating data and the second operating data, that receives user input selecting the first operating data and the second operating data for display, that receives user input selecting a first time period for display, that displays the first data values from the first operating data that have corresponding time values within the first time period and the second data values from the second operating data that have corresponding time values within the first time period together in a graphical display (10, 50) having a common time axis such that the first data values from the first operating data are displayed in the graphical display aligned with the second data values from the second operating data having common corresponding time values, the common corresponding time values being indicated on the common time axis, that displays a thumbnail image corresponding to each set of operating data available for display in the graphical display, each thumbnail image including a graph displaying actual data values represented in the corresponding set of operating data that have common corresponding time values within the first time period, that receives user input selecting a second time period for display, and that updates the graph for each thumbnail image to display the actual data values represented in the corresponding set of operating data that have common corresponding time values within the second time period; wherein each thumbnail image can be selected to display the corresponding set of operating data in the graphical display. a first building system (65, 67, 69, 71, 73) including a first sensor (100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 111) that generates first operating data corresponding to the first building system (65, 67, 69, 71, 73), the first operating data including a plurality of first data values generated by the first sensor and corresponding time values associated with each of the first data values; a second building system (65, 67, 69, 71, 73) including a second sensor (100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 111) that generates second operating data corresponding to the second building system (65, 67, 69, 71, 73), the second operating data including a plurality of second data values generated by the second sensor and corresponding time values associated with each of the second data values; a data server that receives and stores the first operating data and the second operating data over time; a user terminal (168. 169, 170) that accesses the first operating data and the second operating data, that receives user input selecting the first operating data and the second operating data for display, that receives user input selecting a first time period for display, that displays the first data values from the first operating data that have corresponding time values within the first time period and the second data values from the second operating data that have corresponding time values within the first time period together in a graphical display (10, 50) having a common time axis such that the first data values from the first operating data are displayed in the graphical display aligned with the second data values from the second operating data having common corresponding time values, the common corresponding time values being indicated on the common time axis, that displays a thumbnail image corresponding to each set of operating data available for display in the graphical display, each thumbnail image including a graph displaying actual data values represented in the corresponding set of operating data that have common corresponding time values within the first time period, that receives user input selecting a second time period for display, and that updates the graph for each thumbnail image to display the actual data values represented in the corresponding set of operating data that have common corresponding time values within the second time period; wherein each thumbnail image can be selected to display the corresponding set of operating data in the graphical display.