What does level accuracy like 0.5mm/m or 0.029 degrees mean?

It's the manufacturer's stated tolerance: roughly half a millimeter of deviation over a meter of length, which most reviewers consider pro-grade for construction and carpentry. The figure appears in manufacturer and retailer listings for several picks here, but reviewers caution that a spec only matters if the vials stay seated and the frame isn't dropped, so durability matters as much as the headline number.