Why Tolerance Is Minus On Bars For Machining?

Here is an interesting article on the reason for only negative tolerance on drawn bars:
<a href="https://pmpaspeakingofprecision.com/2013/01/29/why-tolerance-is-minus-on-bars-for-machining/" target="_blank" rel="nofollow noopener noreferrer">Why Tolerance Is Minus On Bars For Machining | Speaking of Precision Blog</a>