TTSL is an approximation of loading on any part of the BPA transmission system, based on federal and non-federal generation within the BPA control area, and interchange and wheeling onto the system. It is unadjusted for temperature or streamflow conditions. The date and time of the monthly TTSL peak is used for billing purposes. TTSL is not a typical "end-use" load measure, and is not used as a "system load" measure for any formal regulatory reporting. TTSL data are unavailable prior to 1/1/07.