Reading analog pin

i'm trying understand piece of code written at90usb avr:

code: [select]

int16_t analogread(void)
{
    uint8_t low;
    adcsrb = 0;
    admux  = 0xc0;                // mux input
    adcsra = (1<<aden) | ((1<<adps2) | (1<<adps1)) | (1<<adsc);  // conversion
    while (adcsra & (1<<adsc)) ;
    low    = adcl;                // read lsb first
    return (adch << 8) | low;     // read msb once!
}

i know it's doing read on analog pin (which used calculate battery voltage level), can't figure out which.  being set admux line?

yes, admux register selects analog input.
you can read in datasheet (the full datasheet, not "summary").

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