This lexicon compares, on a scale of 0-10, the use of each term both in the past and in the present, comparing examples and authorities. For each word, the scale indicates, using colours and arrows, the trend of current as compared to past use. An upward arrow indicates that the word is used more now than in the past. Number and colour indicate density of use. Two approaches were adopted in making comparisons with the past: written testimony up to the end of the 19th century, and written testimony up through the first three quarters of the 20th century (at which time authors began writing in the common standard code rather than in the dialects).

The sources used were the following: for the past, the Mitxelena-Sarasola General Basque Dictionary (Diccionario General Vasco); for data on contemporary Basque, the Contemporary Reference Prose corpus (Ereduzko Prosa Gaur), https://www.ehu.eus/euskara-orria/euskara/ereduzkoa/ and the Dictionary of Standard Basque in Contemporary Prose (Hiztegi Batua Euskal Prosan), https://www.ehu.eus/ehg/, both available on the Institute for the Basque Language's website. The Dictionary of Contemporary Basque (Egungo Euskararen Hiztegia) was also used and is available at: https://www.ehu.eus/eeh/.

This part of the project was partially funded by the Basque Government Department of Culture (as of 2008). Funding was also received from the Spanish Ministry of Science and Innovation (HUM2007-29151-E).