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Broadcast History:
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In order to win points, contestants had the option to fill in one letter of the word below the top word or above the bottom word. If they guessed the word correctly, the received one point for every letter in the word they guessed and their team would retain control of the board. A "+" sign next to a word indicated that the point values of that word were doubled.
If a team completed a chain, a new chain would start and the game continued until one team reached 50 points. The winning team then went on to play the bonus round.
This bonus format remained the same throughout the show's 6-month run, but the scoring was changed several time. Initiall, a nearly impossible half-zero scoring format gave the contestant one "half-zero" up to $10,000. The first bonus round of the show's debut, which used this format, enabled the contestant to win just $10. This format was dropped after only one week.

The second scoring format gave contestants $1 to start off with, then added a zero for each correct answer up to $1,000. After that, the next four answers were worth an additional $1,000; the next correct answer won the contestant $10,000. This format, which seemed too easy, was eventually dropped and replaced with a scoring format that gave the contestant $100 for each correct answer up to $900, with the next answer being worth $10,000.

In June 1980, Chain Reaction was cancelled after a 26-week run. The four celebrity guests on the last show played a final bonus game for charity that featured a number of humorous moments. As the series signed off for the final time, Bill Cullen read a humorous chain the producers had assembled as a send-off.
