Code

DateTime targetStartDate = new DateTime(2013, 2, 6);
DateTime targetEndDate = new DateTime(2013, 2, 10);
TimeSpan targetSpan = targetEndDate - targetStartDate;

calendar.EnsureVisible(targetStartDate);

// EnsureVisible does not guarantee that the target date will be at
// the start of the displayed interval, more specifically, if the
// target date is already visible, EnsureVisible does nothing; so
// perform a step-by-step scrolling until the target date is at the start
while (calendar.GetFirstVisibleDate() < targetStartDate)
	calendar.HScrollPos++;

// ...or if you don't need the scroll, you can skip the previous code
// and directly assign targetStartDate and targetEndDate to the Calendar.Date
// and Calendar.EndDate properties
//calendar.Date = targetStartDate;
//calendar.EndDate = targetEndDate;

DateTime first = calendar.GetFirstVisibleDate();
DateTime last = calendar.GetLastVisibleDate();
TimeSpan visibleSpan = last - first;
if (visibleSpan.Ticks == 0)
	return;

double availableWidth = calendar.Width - calendar.ResourceViewSettings.RowHeaderSize;
double pixelsPerTick = availableWidth / visibleSpan.Ticks;
double desiredPpt = availableWidth / targetSpan.Ticks;
double scale = desiredPpt / pixelsPerTick;
scale *= calendar.ResourceViewSettings.TimelineScale;
if (scale < 10)
	scale = 10;
if (scale > 1000)
	scale = 1000;

calendar.ResourceViewSettings.TimelineScale = (int)scale;