Take the 2-minute tour ×  We have been using Scrum for around 9
months and it has largely been successful. However our burndown
charts rarely look like the 'model' charts, instead resembling
more of a terrifying rollercoaster ride with some vomit inducing
climbs and drops.  To try and combat this we are spending more
time before the sprint prototyping and designing but we still
seem to discover much more work during the sprint than initially
thought. Note: By this I mean the work required to meet the
backlog is more involved than first thought rather than we have
identified new items for the backlog.  Is this a common problem
with Scrum and does anyone have any tips to help smooth the
ride?  I should point out that most of our development work is
not greenfield, so we are maintaining functionality in an
existing large and complex application. Is scrum less suited to
this type of development simply because you don't know what
problems the existing code is going to throw up?  Just how much
time should we be spe