A quick, easily portable PHP script to convert nBits to an actual diff.

Altcoins_nBitsToDiff.php

<?php

// Try this with 1d00ffff for a diff of 1 (original Bitcoin mainnet and testnet)
// or 207fffff for 4.6565423739069E-10 (Bitcoin regtest network)

function ConvertBitsToDouble($nBits){
    $nShift = ($nBits >> 24) & 0xff;

    $dDiff =
        (double)0x0000ffff / (double)($nBits & 0x00ffffff);

    while ($nShift < 29)
    {
        $dDiff *= 256.0;
        $nShift++;
    }
    while ($nShift > 29)
    {
        $dDiff /= 256.0;
        $nShift--;
    }

    return $dDiff;
}

$nBits_bitcoin = 545259519;

echo ConvertBitsToDouble($nBits_bitcoin) . PHP_EOL;