What does a + sign next to a test date on a cylinder indicate?

A + sign next to a test date on a cylinder indicates that the cylinder can be filled to a maximum pressure that is 10% above its service pressure. This marking is significant because it reflects that the cylinder has passed its most recent hydrostatic test and meets updated safety standards. The approval to fill to a higher pressure allows for improved efficiency in storage and distribution of gases while maintaining safety protocols. It is essential for ensuring that the cylinder is still safe to use under those increased pressure conditions, thus facilitating more effective utilization in medical and industrial applications.