For the original 4-Point Isochronal #welltest theory in gas wells (#LNG), incremental flow and shut-in pressures needed to reach stabilization. Sequences were thus not necessarily equal in time. This process was lengthy and thus quite impractical. The convenient and practical approach to isochronal testing is equal time periods, called a Modified 4-Point Isochronal Test. Usually four 4 h flow periods segue to a reduced rate extended flow and build-up test. Four 4 h flow & shut-in periods add up to 28 h. In very high deliverability systems shut-in periods can be eliminated, and flow time sequences shortened, typically 2 h works well, so you are done in 8 h. Following pressure transient analysis (#AOF, LIT, #PTA) the #AER expects all tests to be digitally submitted as PAS files.