A low pass filter that approximates a Gaussian transfer function filters the analog bar code signal prior to digitization is used to smooth the bar code signal. A tensioner arm is composed of an elastic band tensioner arm body curved toward a transmission chain and a flexible tensioner shoe which covers the front of the tensioner arm body and which is provided with a chain guide groove to the front of which the transmission chain is slidably fitted. The lower plate is configured for being operatively coupled to the pulley hub. Methods are disclosed for code-rate selection based on successfully decoded blocks as well as incremental parity size selection for retransmission of failed blocks Techniques disclosed here apply to forward-error-correction codes employed for digital data communication systems. 5 to 5; and a second step in which the mole ratio is 2 to 10 and is higher than the mole ratio to be employed in the first step. In step 606, a random number is generated, and in step 607, it is decided that step 608 is to be executed or step 609 is to be executed corresponding to the value of the random number.