How do I do calculation between rows in pandas dataframe group by certain variable?

I have a dataframe like this:

Time      Name     Value
2007Q1    A        30
2007Q2    A        35
2007Q3    A        28
...
2007Q1    B        31
2007Q2    B        50
2007Q3    B        60
...
2007Q1    C        20
2007Q2    C        15
2007Q3    C        30

I want to add another column called Results and perform calculations between each row for each Name. I want to use the value for a quarter divided by the value for the previous quarter and then minus 1, which is similar as Value(Q2)/Value(Q1)-1. Also, I want to group by Name, only do the calculation within the rows with the same name. The results should be like:

Time      Name     Value    Results
2007Q1    A        30       
2007Q2    A        35       0.1667
2007Q3    A        28       -0.2
...
2007Q1    B        31       
2007Q2    B        50       0.6129
2007Q3    B        60       0.2
...
2007Q1    C        20
2007Q2    C        15       -0.25
2007Q3    C        30       1

The starting time period for each ‘Name’ should have no value for Results.

Thanks to everyone who can help!

df['Results'] = df['Value'].div(df.groupby('Name')['Value'].shift()).sub(1)

print(df)
     Time Name  Value   Results
0  2007Q1    A     30       NaN
1  2007Q2    A     35  0.166667
2  2007Q3    A     28 -0.200000
3  2007Q1    B     31       NaN
4  2007Q2    B     50  0.612903
5  2007Q3    B     60  0.200000
6  2007Q1    C     20       NaN
7  2007Q2    C     15 -0.250000
8  2007Q3    C     30  1.000000