(Bloomberg) -- The Swiss National Bank needs to spend roughly 27 billion francs ($30 billion) to keep its currency from appreciating 1.1%, according to a staff paper that offers a rare vignette into what officials may be thinking.

Currency purchases by the central bank “are effective and long-lasting,” and have helped Switzerland avoid a large drop in consumer prices in recent years, Tobias Cwik and Christoph Winter wrote in research published on the SNB’s website on March 28.

While purchases of foreign currency have long been one of the SNB’s tools of choice to keep its haven currency in check, policymakers are typically tight-lipped about the timing and scope of any purchases. While President Thomas Jordan and his colleagues finally raised interest rates above zero last year, the institution’s balance sheet is still much larger than it was a decade ago.

The SNB’s pile of foreign exchange is worth nearly 680 billion francs.

Had it not used negative interest rates between 2015 and 2022, Switzerland’s central bank would’ve needed to spend as much as 550 billion francs on currency purchases to achieve the rate of inflation actually recorded in that time span, according to the research.

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