Books for size charts and grading:
https://www.waterstones.com/author/winifred-aldrich/568014
https://www.williamgee.co.uk/shop/grading-for-the-fashion-industry-book/
https://www.amazon.com/Spec-Manual-Michele-Wesen-Bryant/dp/1563673738
Online resources:
https://www.pointsofmeasure.com/tutorials-education/how-to-create-a-size-chart
https://thelondonpatterncutter.co.uk/pattern-grading/size-charts/
https://successfulfashiondesigner.com/tutorials/how-to-spec-a-garment-for-your-fashion-tech-pack/