I'm always interested in the technical aspects ...

The official post says there is a 30 block retarget time ("- Difficulty re-targets approximately every 30 blocks.")

From our miners, it clearly appears the difficulty is recomputed at each block.
I did not looked much in the code yet to find what algorithm is used, but maybe an explanation here from the dev could help

Continuous difficulty adjustment has pro and con.

• + It prevents the chain to get stuck for a very long time if the hashrate suddently drops. Think about big switching mining pools (middlecoin & co) that can up the difficulty of a not well designed coin to oblivion before letting it rot. The coin *MUST* be prepared to handle these pools
• + It prevents insta mining that concentrate and devaluate the coin. Long retarget times as in bitcoin/litecoin can't be used for newer coins
• - It can cause difficulty instability. Yesterday I observed the difficulty vary between 1 and 2 over very short periods (~10 to 15 blocks maybe). Variations of this amplitude are not a problem, at least at the current state / total hashrate of the coin. But it's hard to predict how it will behave later. Memorycoin2 had very big problems at launch with their difficulty adjustment, lets not reiterate ^^. At long term, strong variations are also a security / sanity concern ... we could imagine miners connected to different instable coins and mining only the easiest blocks of each one
• - If the continuous  adjustment is too slow, it can also cause problems as in yacoin where it allowed insta-mining at the beginning and subsequent dumping.
  

I'm not sure what is currently used, it seems to me that only the time between the last two found blocks is used to compute the next difficulty. If true, this is the root of the instability, more real blocks should be considered (or the capping factor to the diff. adjustment should be reduced.
(the 30 block value seems to appear only as a weighting, preventing extreme change from block to block)

Where is this part of the code coming from ? Another coin that may be facing this problem ? or is it specific to noble ?