code: function updateMetrics() {
  		var dprM;
  
  		isVwDirty = false;
  		DPR = window.devicePixelRatio;
  		cssCache = {};
  		sizeLengthCache = {};
  
  		dprM = (DPR || 1) * cfg.xQuant;
  
  		if(!cfg.uT){
  			cfg.maxX = Math.max(1.3, cfg.maxX);
  			dprM = Math.min( dprM, cfg.maxX );
  
  			ri.DPR = dprM;
  		}
  
  		units.width = Math.max(window.innerWidth || 0, docElem.clientWidth);
  		units.height = Math.max(window.innerHeight || 0, docElem.clientHeight);
  
  		units.vw = units.width / 100;
  		units.vh = units.height / 100;
  
  		units.em = ri.getEmValue();
  		units.rem = units.em;
  
  		lazyFactor = cfg.lazyFactor / 2;
  
  		lazyFactor = (lazyFactor * dprM) + lazyFactor;
  
  		substractCurRes = 0.4 + (0.1 * dprM);
  
  		lowTreshHold = 0.5 + (0.2 * dprM);
  
  		partialLowTreshHold = 0.5 + (0.25 * dprM);
  
  		tMemory = dprM + 1.3;
  
  		if(!(isLandscape = units.width > units.height)){
  			lazyFactor *= 0.9;
  		}
  		if(supportAbort){
  			lazyFactor *= 0.9;
  		}
  
  		evalID = [units.width, units.height, dprM].join('-');
  	}
docs: updates the internal vW property with the current viewport width in px