Compensated nut. They do make you in tune. Test... hit open D then B string third fret. Are you close? Do you want as close to perfect as you can get? Questions? :
Compensated nut - The Acoustic Guitar Forum
GuitarNutCompensation.com
Purpose of square and half moon nut cutouts? : r/Luthier
STL file Compensated Shelf Nut for Guitar・3D printer model to download・Cults
5 Main Types of Guitar Nuts - Main Differences Including Materials Used
Nut compensation - FRETS.NET
Nut compensation - FRETS.NET
Compensated Bone Nut Blanks for Acoustic Guitar - Guitar Templates