I currently have two simple charts that I would like to combine:

a) The first is a stacked column chart that measures the severity of up to
21 different events on a 1 to 4 scale once per month. For example, the column
for March might have 1 severity 4 occurrence, 3 severity 3 occurrences, 5
severity 2 occurrences and 10 severity 1 occurrences against Event type A and
6,11, 9, 2 (respectively) against event type B etc. Each severity level has
a specific colour.

b) The second is a clustered column chart that shows the total number of
events by event type clustered into groups of 3 months. For example, Event
type A might show 19 events in March, 12 in February and 25 in January.

What I would like to do is combine these into a single chart so that each of
the 21 event types (A, B etc.) shows a 3 month history broken down by the 4
severity levels.

I realise that doing this sort of thing is usually dependant upon getting
the data arranged in a specific way, but I haven't been able to work it out
so any help would be appreciated.

Hope this makes some kind of sense!

TIA

Dave