This definition appears very rarely
Samples in periodicals archive:
Statistics South Africa Unit Vale Price Indices 3 Chapter 1: Introduction to the South African export and import unit value indices 1.1 Introduction
Statistics South Africa 6 P0142.7 Export and Import Unit Value Indices, June 2015 Detailed index numbers and rates of change, and contributions
Net barter terms of trade index is calculated as the percentage ratio of the export unit value indexes to the import unit value indexes, measured relative to the base...