is within ... percent of normal

is within … percent of normal is true whenever a sample value is within the reference range for that sample, to within some percentage tolerance. For example, for the case:

egg            22 [5 - 15]            8 [5 - 15]          18 [5 - 15]
milk           24 [

satisfies the condition

egg is within 20 percent of normal

It’s also possible to use the “%” symbol:

egg is within 20 % of normal