In the received data, the FIMS_TIME was recorded by an integer expressed as a multiplicative factor of about 0.00444 seconds every 0.1 seconds, instead of actual time data. To convert these periodic time tags into the actual times, two actual times OBC_TIME were recorded together with FIME_TIME at the beginning and end of the observations (Kwak & Park 2004). By comparing these OBS_TIME with FIMS_TIME values, the actual time during the observations were calculated. If either OBS_TIME or FIMS_TIME (or both) had errors, then the observation duration was compared with the observation schedule to identify the orbit number and calculate the actual times of FIME_TIME.
The quaternion for the FIMS-SPEAR boresight (instrument boresight offset relative to the spacecraft axis) was combined with the quaternion provided by the AF (attitude) file. Then, the location (φ) of each photon event was converted to the coordinates on the sky. WIST (Wide Image Star Tracker) flags were also matched to each event: WIST=1 and WIST=0 corresponding to the events measured during the WIST was on and off, respectively.