I am working with a dictionary where each key contain a list of tuples. It looks like this:

```
dict1 = {'key1': [(time1, value1), (time2, value2), (time3, value3)],
         'key2': [(time4, value4), (time5, value5), (time6, value6)],
         'key3': [(time7, value7), (time8, value8), (time9, value9)], ...}

```

What is wish to do for each key is to find the largest drop in 'valueX' from 'timeX' to 'timeY'.

The tuples are orderes so that 

```
time1 < time2 < time3 

```

And it is (typically) true that

```
value1 > value2 > value3

```

Both things are true for all keys. 

So looking at the first key, what I wish to do is to calculate 

```
value2 - value1 and value3 - value2

```

And save the times that the biggest drop occurs. Let's say that

```
value2 - value1 > value3 - value2

```

Then I wish to save time1 and time2, since it was between those two time values that the largest drop occured.

I am thinking to use a for-loop like the following:

```
for key in dict1:
    for i in dict1[key]:

```

But I cannot figure out how to 

1) loop through the values, calculate the difference between the present value and the past value, save this and compare it the the largest drop that has been observed 

2) to save the times that correspond to the largest drop in 'value'.

I hope you can help me out here. Thanks a lot.