This feature is only available on our Advanced Plan
On the Dashboard, click the edit size chart button for the size chart you want to add to another size chart.
Scroll down to the bottom of the page.
Where it says Parent Size Chart click the dropdown and find the size chart you want to add the current size chart to.
Make sure the parent size chart is lower on the list of size charts in the dashboard than the child size chart or the child size chart will override the parent.
After the parent size chart is set up the child size chart will be associated with all of the products associated with the parent size chart and appear beneath the parent size chart in the popup. There currently isn’t a way to show the parent size chart in the associated products of the child size chart.