This has been a recurrent problem, which is why I would like to share it with you.
Dates are particular values that requires an adequate control over what is being displayed on X-axis. The julianDayNumber converts a date into a number.
methods := RTObject withAllSubclasses flatCollect: #methods.
methods := methods reject: [ :m | m numberOfLinesOfCode > 150 ].
oldestMethod := methods minFor: #date.
b := RTCharterBuilder new.
b extent: 800 @ 200.
b shape circle size: 5; color: (Color blue alpha: 0.1).
b interaction popup.
b points: methods.
b allY: #numberOfLinesOfCode.
b allX: [ :m | m date julianDayNumber - oldestMethod date julianDayNumber ].
b axisConfiguration
noDecimals;
title: 'LOC'.
b axisY.
b axisConfiguration
title: '';
labelRotation: -30;
numberOfTicks: 10;
numberOfLabels: 10;
labelConvertion: [ :v | (Date julianDayNumber: v + oldestMethod date julianDayNumber) ].
b axisX.
b build