On Jan. 1, 1999, European business will wake up to the euro, the single currency devised to take the place of national currencies in 11 countries involved in European monetary union. The good news is that this New Year's hangover is no millennium bug. There isn't likely to be any bad news, either, if companies have prepared their bookkeeping, payroll, database and computer system changes in time. "The euro is going to be a relief," predicted François Deforge of Photonetics Inc. in Wakefield, Mass., whose parent company, Photonetics SA in France, also has subsidiary holdings in Germany and Spain. "As far as trade and financial operations go, this is going to simplify things greatly." He also predicted that the change will help inexperienced companies trade more easily with Europe, because a raft of fluctuating currencies will no longer complicate matters. Those who love their national currencies need not be saddened, because French francs, German marks and Spanish pesetas will circulate for another three years until the euro notes and coins replace them. Meanwhile, companies must keep the books in parallel versions of national currencies and euros. The single currency is expected to sharpen competition throughout Europe as a result of cheaper transaction and information costs, stable exchange rates and transparent price differences. Yet photonics managers do not envision a series of cross-border mergers nor a reshuffling of supply arrangements. However, firms could face one ticklish problem: adjusting their price lists. After the euro arrives, buyers across Europe will be able to compare price lists, making differences between countries obvious. Dirk Basting, president and CEO of Lambda Physik Inc. in Fort Lauderdale, Fla., predicted that, in the long term, sales representatives may get the worst of the change. Currently, manufacturers often have a different agent in each European country. But Basting thinks that the euro will make it easier for companies to sell directly. Analysts also expect that a pan-European capital market will lead to corporate restructuring. For exporters, importers and multinationals with experience in foreign exchange, the euro will be a welcome change. "Trading with foreign currency is like learning a foreign language," Deforge pointed out. "The first one is the hardest."