NU Series Digital Clocks 
They are of robust manufacture in a steel case intended for industrial applications and can be made to order offering a wide range of options as Timers and as Clocks.
As clocks they support either standalone operation as slaves on a network where multiple clocks must all display the same time.
In network mode one clock can act as the Master Clock to synchronises all the slave clocks or a system consisting of slave clocks can be interfaced with a PC so the clocks will all display PC network time.
In independent Master Mode, the Control clock can perform automatic (unattended) NZ DST.
The picture shows (on top) a 5 digit timer with 4-inch high digits which was ordered to time sports events. This particular model counts up from 0:00:00 to 9:59:99. (0-9 minutes, 0-59 seconds, 0-99 hundredths of seconds) for precise timing.These particular Timers were further specified to run off 12VDC (car battery) from a cigar lighter connection with a separate 230V adapter for when mains power might be available and the Timer came with a 5m control cable to a hand-held control box featuring Start/Hold/Reset switches. The cables are removable for transporting and connect via plugs which can be seen on the top of the Timer.
The lower display is a 6 digit clock with 6 inch high digits. This is a large double sided clock which was one of several ordered for installation on a marine wharf at a major passenger terminal. The clock features side buttons which are used to set the time. It is quite heavy and was designed with hanging lugs for a chain..
Q & A
What protocol for networking multiple clocks?
THE CLOCKS WORK ON RS485 PROTOCOL. THE DISTANCE BETWEEN EACH CLOCKS CAN BE UPTO (500~1200) MTRS.
How do you network multiple clocks so they all keep exact same time)
ONLY TWO WIRES NEEDED FOR LOOPING ALL CLOCKS.
Do you have independent Master Clock Controller which can correct these clocks?
IF PC IS CONNECTED THEN PC WILL BE MASTER ELSE Master Clock.
NOTE ALL CLOCKS CAN BE RUN INDEPENDENTLY AND CAN ACCEPT COMMAND BY MASTER.THEY CAN BE RESET BY THEMSELF OR MASTER.
FUTHER IF YOU HAVE QTY. THEN WE CAN DEVELOP/MODIFY ACCORDING TO YOUR NEED.