How is Index Error described when it is a negative value between 0-5?

Index Error refers to the discrepancy between the actual reading of a device and the true position it indicates. When this error is described as a negative value between 0 and 5, it indicates that the reading is not aligning with the expected position on the arc of the device being used for navigation.

In this context, "off the arc" means that the actual reading falls short of what is encountered around the arc, typically indicating an error in the calibration or alignment of instruments such as a compass or a sextant. This kind of error can lead navigators to miscalculate their position if not accounted for, leading to potential misdirection in navigation.

Understanding Index Error is crucial, as maintaining accuracy in navigation instruments is vital for safe and effective sea navigation. Knowing that a negative Index Error indicates that the instrument is reading too high, being "off the arc" helps navigators to make necessary adjustments to their calculations and navigation practices.