Index number and Order number

Index number noun - A number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time.

Order number and index number are semantically related in ordinal number topic. In some cases you can use "Order number" instead a noun phrase "Index number", when it comes to topics like serial number.

Index number and order number are semantically related in ordinal number topic. You can use "Index number" instead a noun phrase "Order number", if it concerns topics such as serial number.