If you start at 70/30 and stocks drop by 10% while bonds hold steady, then you're at about 67.7% stocks and 32.3% bonds. Getting to a 71/29 balance at that point requires that you add much more than 1% to your stock position.

You'd probably do okay just to rebalance back to 70/30 periodically - once per quarter or once a year.

Yeah, but the thing is that numerous studies have shown that rebalancing has virtually no long-term effect.

Shortly after I retired I downloaded a bunch of articles & papers & studies about rebalancing.

Typical is this paper:
Asset Allocation, Rebalancing and Long-Term Investment Returns(updated July 2007)
"... Once again, portfolio returns and volatility differed very little as a function of rebalancing frequency. Contrary to some opinion, rebalancing frequency mattered little, and didn't increase volatility. In this case, frequent rebalancing actually increased volatility slightly for this 29 year period, 10.71% for quarterly rebalancing compared to 10.31% for biyearly rebalancing."

From the same paper:
"Truman Clark, of DFA, examined the issue of rebalancing in detail in three papers published online in Fall of 2001. He concluded that, "the proposition that a rebalancing strategy can increase expected return is dubious," and that "rebalancing costs definitely reduce expected returns."