+// static int16_t distances[N_SENSORS];
+
+// hold_regs[0] is unit ID
+#define thresholds (hold_regs+1)
+#define led1_sensors (hold_regs[13])
+#define led2_sensors (hold_regs[14])
+
+#define led_bitmap (hold_regs[MB_N_HOLD_REGS_EEPROM])
+#define distances (hold_regs+MB_N_HOLD_REGS_EEPROM+1)
+#define free_bitmap (hold_regs[MB_N_HOLD_REGS_EEPROM+13])
+#define err_bitmap (hold_regs[MB_N_HOLD_REGS_EEPROM+14])
+#define max_distances (hold_regs+MB_N_HOLD_REGS_EEPROM+21)
+#define err_counts (hold_regs+MB_N_HOLD_REGS_EEPROM+41)