The metrics are used for different things in different contexts: coordinate base units, anchor offsets, grid column/row weights, paddings, etc. The interpretation of the units used in the metric depends on the context, the type of Layout in which they are used, etc. Usage:

        TAlfMetric metricX(1.0, EAlfUnitNormalized); 
 TAlfMetric metricY(2.0, EAlfUnitNormalized);
 //Set Layout base unit using Metrc
 layout->SetBaseUnit(metricX);
 
 //Create XYMetric using Metric 
 TAlfXYMetric metricXY(metricX, metricY);
 //Set Layout base unit using XYMetrc
 layout->SetBaseUnit( metricXY );
 
 //Create Anchor offset as boxMetric
 TAlfBoxMetric offset(
       TAlfMetric(0.1, EAlfUnitMySize),
       TAlfMetric(-0.1, EAlfUnitMySize),
       TAlfMetric(0.1, EAlfUnitMySize),
       TAlfMetric(-0.1, EAlfUnitMySize));
 TAlfAnchorAttachmentOrigin attachmentOrigin(EAlfAnchorAttachmentOriginNone);
 TInt attachmentOrdinal(EAlfAnchorAttachToParent);
  
 //Attach anchor origin
 anchorLayout->Attach(ordinal, offset, attachmentOrigin, attachmentOrdinal);