EVERY weekday The Economist explains a new subject, topical or timeless, profound or peculiar. As the end of the year approaches, we look back at the explanations that have proved most popular with readers during 2015. (Normal service will resume on January 4th.)

ON FRIDAY, the Swiss National Bank (SNB), Switzerland’s central bank, reported second quarter losses of SFr20 billion ($20 billion). Following an equally bad first three months of the year, the SNB’s losses so far for 2015 now amount to a whopping SFr50.1 billion, equivalent to 7.5% of Switzerland’s GDP.

FOREIGN skiers were bound to suffer. So was the Swiss economy, most assumed, after the Swiss National Bank (SNB) suddenly abandoned the Swiss franc’s peg to the euro in January. The franc rose by 30% against the euro in a matter of minutes, and remains about 15% higher than it was. This made Swiss exports more expensive for foreigners, and foreign goods cheaper for the Swiss.

CONTEMPORARY central banking is a strongbox of oddities. Deposits, which normally pay interest, can now incur a charge. Investments in government debt, which normally offer a return, give a negative yield. Faced with this weirdness central banks are trying to respect some cardinal rules of finance, with the Swiss National Bank (SNB) and the European Central Bank (ECB) taking steps to protect themselves from losses and ensure that their balance-sheets add up.

SWISS voters used to hold their central bank in high esteem: one survey in 2013 found the Swiss National Bank (SNB) to be their most respected national institution. That may change after its shock decision on January 15th to abandon the Swiss franc’s cap against the euro. The franc instantly shot up by 30%, provoking howls of anguish from Swiss firms.

WHEN the Swiss National Bank (SNB) intervened to weaken its currency in 2011, analysts called the subsequent abrupt drop in the franc’s value a “20-standard-deviation move”. Assuming the franc’s ups and downs follow a normal distribution, such a big shift should not have occurred again for many squillions of years.

ON THURSDAY January 15th Switzerland’s central bank, the Swiss National Bank (SNB), removed the cap on its currency, which it had imposed over three years ago and reaffirmed only three days before its repeal. The doffing of the cap surprised and upset the foreign-exchange markets, hobbling several currency brokers, including Alpari (which happens to sponsor the London football team I support).

INVESTORS checking out the Everest Capital website will find that the hedge fund offers strategies that are diversified across themes, countries and sectors. So they wouldn’t have expected losses from any one bet to be that significant. But over the weekend, it was revealed that last week’s surge in the Swiss franc had virtually wiped out the group’s main fund, Everest Global Capital.

IN THE world of central banking, slow and predictable decisions are the aim. So on January 15th, when the Swiss National Bank (SNB) suddenly announced that it would no longer hold the Swiss franc at a fixed exchange rate with the euro, there was panic. The franc soared. On Wednesday one euro was worth 1.2 Swiss francs; at one point on Thursday its value had fallen to just 0.85 francs.

ANXIETY at the Swiss National Bank’s surprise decision today to drop its peg against the euro was nowhere more evident than in central Europe. The Swiss franc soared against all the region’s currencies, including the euro, the Hungarian forint and especially the Polish zloty, and stock exchanges in Poland (pictured) and Hungary dropped sharply.

CURRENCIES don’t normally move that far on a daily basis—2 to 3% is a big shift. The exception is when a country on a fixed exchange rate suffers a devaluation; then a 20-30% fall is a possibility. But a 20-30% plus upward move is almost unprecedented. That, however, is what happened to the Swiss franc on January 15th, as Switzerland’s central bank abandoned its policy (instituted back in 2011) of capping the currency at Sfr1.20 to the euro.

THE Swiss franc is a volatile currency that is fast becoming worthless. That, at least, is what some members of Switzerland’s right-wing People’s Party (SVP) would have you believe. Thanks to the SVP, Switzerland will vote on November 30th on a radical proposal to boost the central bank’s gold reserves. Bigger reserves, activists argue, will make the Swiss economy more stable and prosperous. In fact the opposite is true.

SOVEREIGN wealth funds, typically set up by oil-exporting nations, have been around for decades, in the case of Kuwait since 1953. But their influence has increased in recent years, as China has adopted a similar strategy for investing some of its vast foreign-exchange reserves while existing funds have been fuelled by gains from high oil prices.

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Brazil’s finance minister coined the term “currency wars” in 2010 to describe how the Federal Reserve’s quantitative easing was pushing up other countries’ currencies. Headline writers and policy makers have resurrected the phrase to describe the Japanese government and central bank’s pursuit of a much more aggressive monetary policy, motivated in part by the strength of the yen.The clear implication of the term “war” is that these policies are zero-sum games: America and Japan are trying to push down their currencies to boost exports and limit imports, and thereby divert demand from their trading partners to themselves. Currency warriors regularly invoke the 1930s as a cautionary tale. In their retelling, countries that abandoned the gold standard enjoyed a de facto devaluation, luring

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IT IS starting to look like a sustained attack. On January 4th an article in Die Weltwoche, a Swiss weekly magazine, accused Philipp Hildebrand, president of the Swiss National Bank (SNB), of personal currency speculation while the SNB was intervening to stabilise the Swiss franc/US dollar rate.

On Tuesday, the Swiss National Bank (SNB) adopted a bold policy of pledging to sell Swiss Francs in an unlimited amount to ensure that the exchange rate viz-a-viz the euro is at least 1.2 Swiss Francs per euro. The exchange rate promptly jumped over 8 percent to a bit more than 1.2 Swiss Francs per euro. The SNB can clearly weaken its currency in this way, so long as its commitment is unwavering.

WHEN the going gets tough, the tough buy Swiss francs. That was true in the 1970s, when the Swiss were forced to impose negative interest rates on foreign depositors. And it has been true in recent years, with Switzerland’s currency rising by 43% against the euro between the start of 2010 and mid-August this year.

CENTRAL banks have historically been regarded as the guardians of a currency’s value, but occasionally they want to drive their exchange rates down. Rarely have they acted as aggressively as the Swiss National Bank (SNB) did on September 6th.