A host write based write ordering mechanism is used so the write ordering on the secondary system is derived from the write ordering applied by the host to the primary system. Since there takes place no gap between the front edge of the rear plate portion and rear edge of the front plate portion, the conveyor chain thus constructed can convey products more stably without thrust-up, stalling or overturn of them. NADH concentration may conveniently be measured by Optical Density. The gas bubble is formed at both sides of the heater. The conductive layer is an n-electrode. The preferred spout does not use any O-ring members, which are prone to failure when used with gasoline, but instead uses a slidable sleeve with inner and outer seal surfaces provided by a flared or bell-shaped seal member.