A battery gives the urnas, as these portable electronic voting machines are called, a backup in case of power failures. Voters punch in several digits to vote — and are no longer obliged to write out a candidate's name, a baffling chore for borderline literates. While criticism grows in the United States over electronic voting machines, Brazil has won praise for its affordable and uniform voting-machine system. Latin America's biggest democracy has exported its electoral know-how to Argentina, Mexico and the Dominican Republic. A spokesman for the electoral commission here says the government has also advised India and the Ukraine on election procedures. Designed by the government, the machines were made by Unisys and ProComp, a Brazilian company since acquired by Diebold Election Systems. Though computer scientists in the United States have vociferously criticized Diebold's machines for being vulnerable to tampering, Brazil's urnas have generated mostly laudatory PR buzz. Printers have been affixed to a small number of the machines, producing an auditable paper trail. That voting-machine model is “definitely the right idea,” said Dan Wallach, a computer science professor at Rice University. Wallach co-authored the first expert report criticizing Diebold, which launched the electronic-voting controversy on a wide scale in the United States. “The machines give you transparency. You can't joke with them,” said Carol Majewski, head of a Porto Alegre lawyers association that used 137 of the machines to elect its officers. Even high-school student councils will soon use urnas, said 20-year-old Claudio Luiz, a computer programmer at the Tribunal Regional Eleitoral in Rio Grande do Sul. He said the machines are “faster and safer” than old-style paper voting. Still, Brazil's urnas are not infallible. Human, hardware and software failures led officials to discard results in a handful of cases in last year's presidential election. And in what critics call a major setback to the movement for voting transparency, a new law approved in October will do away with printed e-voting receipts. A small group of computer scientists and other activists are demanding that all urnas be equipped with printers. “What is the point of this technology if they cannot be trusted?” asked Michael Stanton, a British-born Brazilian computer science professor at the Universidade Federal Fluminense. A move toward printed ballots began unfolding three years ago, when advocates demanded the machines be equipped with a paper trail. The plan was to outfit nearly 12,000 electronic voting machines with printers, enabling voters to look at a paper receipt after placing their ballots. The paper is shielded by a glass screen, then dropped into a sealed plastic bag that's firmly affixed to the machine. But in last year's presidential election, just 3 percent of all precincts used printers, election officials said. Government representatives say that doing away with the printers will save Brazil about $100 million. The key advantage, though, is that printerless machines will speed up the voting process, said spokesman Paulo Cesar Camarao. “Paper itself offers no guarantee of a transparent election,” he said, adding that printers often suffer technical problems in Brazil's tropical and subtropical climate. Last year, printers delayed elections by 12 hours in a handful of municipalities, he said.