Unexplained Conversion from a binary/hex within code

I am using code from the Waveshare website ( for use with the ADDA Waveshare board put on a RPi3 ) : http://www.waveshare.com/wiki/File:High-Precision-AD-DA-Board-Code.7z

*********************************************************************************************************
*   name: main
*   function:  
*   parameter: NULL
*   The return value:  NULL
*********************************************************************************************************
*/

int  main()
{
    uint8_t id;
    int32_t adc[8];
    int32_t volt[8];
    uint8_t i;
    uint8_t ch_num;
    int32_t iTemp;
    uint8_t buf[3];
    if (!bcm2835_init())
        return 1;
    bcm2835_spi_begin();
    bcm2835_spi_setBitOrder(BCM2835_SPI_BIT_ORDER_LSBFIRST );      // The default
    bcm2835_spi_setDataMode(BCM2835_SPI_MODE1);                   // The default
    bcm2835_spi_setClockDivider(BCM2835_SPI_CLOCK_DIVIDER_1024); // The default
    bcm2835_gpio_fsel(SPICS, BCM2835_GPIO_FSEL_OUTP);//
    bcm2835_gpio_write(SPICS, HIGH);
    bcm2835_gpio_fsel(DRDY, BCM2835_GPIO_FSEL_INPT);
    bcm2835_gpio_set_pud(DRDY, BCM2835_GPIO_PUD_UP);        
    //ADS1256_WriteReg(REG_MUX,0x01);
    //ADS1256_WriteReg(REG_ADCON,0x20);
    // ADS1256_CfgADC(ADS1256_GAIN_1, ADS1256_15SPS);
    id = ADS1256_ReadChipID();
    printf("\r\n");
    printf("ID=\r\n");  
    if (id != 3)
    {
        printf("Error, ASD1256 Chip ID = 0x%d\r\n", (int)id);
    }
    else
    {
        printf("Ok, ASD1256 Chip ID = 0x%d\r\n", (int)id);
    }
    ADS1256_CfgADC(ADS1256_GAIN_1, ADS1256_15SPS);
    ADS1256_StartScan(0);
    ch_num = 8; 
    //if (ADS1256_Scan() == 0)
        //{
            //continue;
        //}
    while(1)
    {
        while((ADS1256_Scan() == 0));
        for (i = 0; i < ch_num; i++)
        {
            adc[i] = ADS1256_GetAdc(i);
            volt[i] = (adc[i] * 100) / 167;    
        }

        for (i = 0; i < ch_num; i++)
        {
            buf[0] = ((uint32_t)adc[i] >> 16) & 0xFF;
            buf[1] = ((uint32_t)adc[i] >> 8) & 0xFF;
            buf[2] = ((uint32_t)adc[i] >> 0) & 0xFF;
            printf("%d=%02X%02X%02X, %8ld", (int)i, (int)buf[0], 
                   (int)buf[1], (int)buf[2], (long)adc[i]);                

            iTemp = volt[i];    /* uV  */
            if (iTemp < 0)
            {
                iTemp = -iTemp;
                printf(" (-%ld.%03ld %03ld V) \r\n", iTemp /1000000, (iTemp%1000000)/1000, iTemp%1000);
            }
            else
            {
                printf(" ( %ld.%03ld %03ld V) \r\n", iTemp /1000000, (iTemp%1000000)/1000, iTemp%1000);                    
            }

        }
            printf("\33[%dA", (int)ch_num);  
        bsp_DelayUS(100000);    
            }   
    bcm2835_spi_end();
    bcm2835_close();

    return 0;
}

Please help me figure out what this piece does in the main():

for (i = 0; i < ch_num; i++)
{
    adc[i] = ADS1256_GetAdc(i);
    volt[i] = (adc[i] * 100) / 167; 
}

The constants (being 100 and 167) are not explained. What exactly are they trying to do in this 'calibration' and what do these constants depend upon?

Learning to read datasheets is an important skill for embedded programming.

The ADC on this chip returns a 24 bit signed value. The datasheet says

The ADS1255/6 full-scale input voltage equals ±2VREF/PGA.

Full-scale is 0x7FFFFF or 8388607.

I believe VRef is 2.5V, and the code sets PGA to 1 with ADS1256_CfgADC(ADS1256_GAIN_1, ADS1256_15SPS);

So an adc[i] value of 1 represents 1/0x7FFFFF of (2*2.5/1)Volts or 0.596 microvolts. We can convert the raw reading to microvolts by multiplying by 5000000 / 8388607. By multiplying by a number that large would overflow a 32 bit int, so let's reduce.
5000000 / 8388607 ~= 500/839 ~= 100/167.

(It would be possible to get a little more precision without overflow by multiplying by 250/419)