Implantable medical devices are adapted for developing a vectorcardiograph from signals across pairs of electrodes. The volatile memory includes a number of tables containing information related to the flash memory storage, including a table storing physical flash memory addresses and a plurality of tables containing metadata. The method is applicable to high-volume low-cost manufacturing of MEMS safety-and-arming devices. An internal wall is mounted within a front portion of the housing and divides the housing into an upper passage and a lower passage.