That's the problem; it's not a modern system. eg, the British GPO 332 handset was first issued in 1937 - and still works. It's difficult to demand millisecond

That's the problem; it's not a modern system. eg, the British GPO 332 handset was first issued in 1937 - and still works. It's difficult to demand millisecond timing when you're backwards-compatible with pre-war equipment.