This model represents measures as first class objects, that is, an object that encapsulates a number with its unit. This representation allows the programmer to use measures in arithmetic expressions as if they were numbers, but with the advantage of providing explicit information to the system, specifically, the measures units. See http://dl.acm.org/citation.cfm?id=1094964 or http://stephane.ducasse.free.fr/Teaching/CoursAnnecy/0506-M1-COO/aconcagua-p292-wilkinson.pdf for more about this.
Download a fresh Pharo image (http://www.pharo.org) and in a workspace do-it this:
Metacello new
baseline: 'Aconcagua';
githubUser: 'mtaborda' project: 'aconcagua' commitish: 'v4.1.0' path: 'repository';
load
Metacello new
baseline: 'Aconcagua';
githubUser: 'mtaborda' project: 'aconcagua' commitish: 'v5.0.0' path: 'repository';
load
go-to => https://github.com/ba-st/aconcagua