This reports the AC mains frequency this module was designed to operate on, in units of 0.1Hz, 500 for a 50Hz-rated module, 600 for 60Hz, the reference figure behind the notSync assessment in tsiModuleACInState and the raw reading in tsiModuleACinFreq. In regions where 50Hz and 60Hz equipment might coexist or where a module could be misrouted to the wrong region, a module built for the wrong nominal frequency would constantly flag notSync even on a perfectly healthy local grid. An admin troubleshooting a persistent notSync status on an otherwise-healthy AC feed would check this field first to rule out simply having the wrong-frequency module installed for the region.