A debt anchor can be defined in a few ways. It could be the absolute level of debt or it could be the debt in proportion to the size of the economy. The government has chosen to opt for the second version: federal debt as a proportion of the economy. The government's stated goal is for the debt to stand at 31.9% of GDP.
One can reach that by adjusting the level of debt or accumulated deficits. It can also stimulate the economy or slow it down—a very unlikely event—because it's a denominator and a numerator: the debt divided by GDP. Of course, if the GDP grows faster, you don't need to do that much with the debt to make it represent a smaller share of the economy. That's the type of anchor the government has chosen.