hello std dev is the square root of the variance. assume we measure lenghts of something normally distributed. we use millimeter. we calculate our variance to be 100mm and thus std dev to be sqrt(100)=10mm but, if we instead would measure the same objects in meter, then we'd get the variance to be 0.1m (exactely the same as 100mm) but then the std dev is sqrt(0.1)=0.3162 which is 316mm! so have our std dev suddenly increased from 10mm to 316mm just by using a different scale when measureing the same objects?