ERNIE generates random numbers and these are later matched to a list of bond holders to produce the winners each month.

This extract from a research document from 1958 explains the principle:

"The machine which has been designed to generate the list of random numbers for the monthly draws of Premium Bonds is known as the Electronic Random Number Indicator Equipment or ERNIE. It uses the random voltages generated at the terminals of cold-cathode tubes as its primary source of random events, two such sources contributing to each character of the nine-digit number provided by the machine. The complexity of the machine arises from the need to avoid any correlation between the digits of each number or between the numbers themselves. The high degree of reliability demanded of the machine and the speed of operation required of its counters is such that special core/transistor circuits had to be introduced on a fairly large scale although other parts of the machine use more conventional techniques. The output of the machine is fed to page printing teleprinters since although ERNIE can operate at much higher speeds than those required for teleprinting, no other suitable printer is commercially available in sufficient quantity at an economic price and with the same reliability."

A weekly jackpot prize of £25,000 (drawn on a Saturday) was introduced in September 1968 and the first winning bond was 5RS 662663. This weekly draw was scrapped in favour of a larger monthly draw and so a £1 million jackpot prize was introduced in April 1994 to compete with the football pools and to retain investors.

By the 21st century, ERNIE was as popular as ever with the maximum holding limit at £20,000, the minimum purchase £100 and the smallest prize drawn was £50.

From May 2003, the maximum holding limit was increased to £30,000. At the same time the odds of a single bond winning a prize were lengthened to 30000 to 1. From September 2004, the odds changed to 24000 to 1.

Premium Bond numbers are only issued once, and as sales of bonds have increased over the years, the range of numbers eligible for a prize is wider than ever. To cope with this spread, from June 2005 new Premium Bonds had 11 digits . ERNIE, mark 4, introduced in April 2004 is able to generate 9, 10 or 11 digit numbers, so that all bonds regardless of when they were purchased have an equal chance of becoming a winning number!

The output of each draw is checked independently by the Government Actuary’s Department (GAD). It uses four methods of testing – Frequency, Serial, Poker and Correlation – to make sure the output has followed no set patterns, because any set pattern would suggest a bias. If no such pattern is discernible then the draw is determined to be random. A certificate is issued by GAD to verify the randomness of the draw.

ERNIE 1

	ERNIE 1 ERNIE was designed and built in the Research Branch of the Engineer - in - Chief's Office of the Post Office and was installed at Lytham St. Annes by staff of the Preston Telephone Area.

ERNIE 2

	ERNIE 2 Into the computer age: the new ERNIE, built in 1973 took only 6 hours to run a draw and could easily cope with the increasing range of numbers, as premium bonds became more popular both as an investment and a bit of fun.

ERNIE 3

	ERNIE 3 A much streamlined ERNIE came into being in 1988 although the principle of generating random numbers has remained unchanged.

ERNIE 4
The power behind Premium Bonds

	ERNIE 4 Today, ERNIE is a commercially produced chipset on a printed circuit board. He can generate more numbers, faster than ever before. ERNIE is still the power behind Premium Bonds.

Links & References
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