Kimoto’s Gravity Well (KGW) is a modification to Bitcoin’s difficulty adjustment algorithm that was first developed for the altcoin ‘megacoin’ and has since been implemented in many other altcoins, both in its initial incarnation as well as in modified fashions. Whereas Bitcoin averages the last 2016 blocks to determine difficulty retargeting, KGW retargets difficulty at every block. This technique was developed to address what began occurring to various altcoins when multipools first began to emerge.
A multipool mines different coins, generally based upon profitability, and switches between those different coins, often in rapid succession. Because this methodology provides miners with higher returns, their size and mining power quickly grew. What this meant for altcoins with smaller mining networks was that once a multipool came and went, a spike in difficulty could leave standard miners working for days, weeks, or months to mine enough blocks to trigger the next difficulty retarget. KGW in essence smoothes out the retargeting of mining difficulty to allow for conditions where large amounts of hashing power come and go on a network without causing major disruptions to the timing intervals between mined blocks.