What is a word that means one-based index?

As opposed to zero-based. This is in a context where index would certainly be interpreted as zero-based. Some possibilities: count, number, numbering, ordinal. But I'm not sure which of these, or another word altogether, would be the most clear.

Count also has the disadvantage of being easy to confuse with "number of entities inside or related to the referred entity" as opposed to "number of entities before the referred entity, plus one".

By way of explanation, in the following list [A, B, C, D, E], the zero-based index of C is 2, while the one-based index of C is 3.

Solution 1:

If you want to be consistent with technical terms used in math,

• For zero-based index: Nonnegative Index
• For one-based index: Positive Index