Experiment to register gym progress

Following Goethe's advice to attend to the present moment, I've been itching to change the way in which I register my gym progress. The first part of this puzzle is a widget that allows me to register two dimensions and the same time, and that also has discreet steps. The purpose is to be able to register both weight and reps lifted with a single gesture.

Now, suppose you keep within the 8-12 rep range, and your dumbbells come in increases of 2.5Kg, now it would look like this:

var sexier = new Sexy({
  el: document.getElementById("gymrat"),
  min: { x: 5, y: 8 },
  max: { x: 15, y: 12 },
  step: { x: 2.5, y: 1 },
  value: {x: 10, y: 10},
  onChange: function(){...}
});