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I am interested in looking at children's birthweight across the waves from 2010 and onwards. I have come across various children's birthweight variables but am failing to understand the difference between some. In the newborn dataset, they include variables c_bwt, c_bwtlb, c_bwtoz, c_bwtk, c_bwtg5 for the child's birth weight. It also includes c_chdnbub_lw and c_chdnbub_xw which are indicated as newborn birthweight. I am not sure what the difference is between the first 5 variables and the last two variables. In addition, what are the units of measurement for the last two variables I was not able to find that information? Thank you.