The Base PM Date field on the Biomed window relates to the Biomed Make/Model feature. It is used solely for the creation of new PM Schedules copied from Biomed Make/Model. If the associated Biomed Make/Model has a PM Schedule, the Base PM Date field is required on the Biomed window in order to calculate the next PM date.
PM Schedules are copied from the Biomed Make/Model record, and WebTMA uses the difference in days between the Base PM and PMs on the Biomed Make/Model window and applies the difference to the Base PM Date on the Biomed record to calculate the next PM date on the Biomed / PMs Tab.
When the PM Schedules are copied, the offset is applied to the Next PM Date field so the PM Schedules have a relevant next date.