In an effort to further the development of e-commerce, the federal Electronic Signatures Act (2000) established uniform national standards for determining the circumstances under which contracts and notifications in electronic form are legally valid. Legal standards were also specified regarding the use of an electronic signature ("an electronic sound, symbol, or process, attached to or logically associated with a contract or other record and executed or adopted by a person with the intent to sign the record"), but the law did not specify technological standards for implementing the act. The act gave electronic signatures a legal standing similar to that of paper signatures, allowing contracts and other agreements, such as those establishing a loan or brokerage account, to be signed on line. Once consumers' worries eased about on-line credit card purchases, e-commerce grew rapidly in the late 1990s. In 1998 on-line retail ("e-tail") sales were $7.2 billion, double the amount in 1997. On-line retail ordering represented 15% of nonstore sales (which included catalogs, television sales, and direct sales) in 1998, but this constituted only 1% of total retail revenues that year. Books are the most popular on-line product order—with over half of Web shoppers ordering books (one on-line bookseller, Amazon.com, which started in 1995, had revenues of $610 million in 1998)—followed by software, audio compact discs , and personal computers . Other on-line commerce includes trading of stocks, purchases of airline tickets and groceries, and participation in auctions.