Pooled variance is the arithmetic mean of a number of variances. Due consideration is being given to their respective degrees of freedom.
If s1^2 , s2^2 , s3^2 …… sk^2 are estimates of variances and n1, n2, n3, …, nk their respective degrees of freedom, then pooled variance S2 is given as
Standard uncertainty uA= S
Source: measurement uncertainty
