According to the present invention, a PCR device including two heating blocks which is used for nucleic acid amplification reactions is disclosed. One such apparatus can include a dithering circuit configured to generate a sequence of numbers that exhibit statistical randomness and a variable frequency circuit configured to adjust a frequency of an output based on the sequence of numbers so as to spread energy of spurious tones in a frequency response of the output to lower a noise floor. The leading edge of the replacement blade is positioned circumferentially for support only by the platform extension thereby limiting the mean and vibratory stresses in the leading edge of the airfoil and maximizing damage tolerance. The lacrosse head can also include a stiffening member attached to the scoop and a sidewall of the frame, and a collared male plug for joining the frame to a hollow shaft.