Ask HN: Why debttothepenny hasn't moved more than +/- a billion since 3/15/17?

Why hasn't the treasury's measure of debt "to the penny" [1] changed significantly since 3/15/17.

[1] https://www.treasurydirect.gov/NP/debt/search?startMonth=01&startDay=01&startYear=2017&endMonth=09&endDay=28&endYear=2017