OK, for trading, it is interesting that Big Fat Springs (like...

OK, for trading, it is interesting that Big Fat Springs (like the one above) are not considered as reliable or strong (in general), as little tiny fine springs.
And big fat springs force you to to hold more risk on an entry, as the stop would generally be placed below the low of the spring (much wider than a little tiny spring).

Personally, I probably would not take an entry on that spring (above), as firstly - it is a big fat spring, and secondly - it is in a downtrend.
And if you look at it, the spring has already done its best for now, and is potentially already turning down (it probably wasn't very strong because it is in a downtrend). Usually when you enter on a spring, you are just taking the initial ride (like a scalp), although an entry on a large timeframe may be held longer.
That said, you may get a second chance, as it appears that price (on the chart above) may come down and 'test the spring', which is where price will again test the strength of the back line you have drawn.

The test of a spring, and sometimes even a secondary test of a spring, are also legitimate long entry set ups, although in a downtrend, their strength should also be discounted (and they can also just fail at times, especially in downtrends, and after serious weakness).

Stop loss placement is a subject in itself, usually it is under price structure, but can also be a measured amount like ATR

cheers