The arduino A/D sampling the signal in 10-bits of information but the output should be in terms of 8-bits. Moreover, the chip produces noise also when there's no signal at all, therefore values below the noise level should be nullified. These code lines make sure the 10-bit value will be over the noise level and mapped into an 8-bit value. The code was working as it should and now I was ready to continue to the integration.