Before 1961, the standard for atomic masses was the isotope ¹⁶O, to which physicists assigned a value of exactly 16. At the same time, chemists assigned a value of exactly 16 to the naturally occurring mixture of the isotopes ¹⁶O, ¹⁷O, and ¹⁸O. Would you expect atomic masses listed in a 60-year-old text to be the same, generally higher, or generally lower than in this text? Explain.