I've been reading up on moving average calculators such as SMA, EMA etc and how they are used to indicate trend reversals.
One question I'm having trouble finding the answer to is: how do you decide the length of time to set them to?
The 'standard' seems to be 10 days for the short term SMA and EMA, and 30 days for the long term.
What would cause a trader to alter these settings? For example, when would these settings not be appropriate?