[Python] How to calculate with MultIndex?

I have a Pandas DataFrame with coordinates values (X,Y), temperatures (T) and measurement results (H)

df=pd.DataFrame([
{'X':0,'Y':0,'T':25,'H':1.2},
{'X':1,'Y':0,'T':25,'H':1.3},
{'X':0,'Y':1,'T':25,'H':1.4},
{'X':1,'Y':1,'T':25,'H':1.5},
{'X':0,'Y':0,'T':125,'H':2.2},
{'X':1,'Y':0,'T':125,'H':2.4},
{'X':0,'Y':1,'T':125,'H':2.6},
{'X':1,'Y':1,'T':125,'H':2.8},
])
df=df.set_index(['X','Y','T'])


Now I would like to calculate the difference of the measurements at the temperatures of each coordinate point: H(T=125)-H(T=25) So I would like to get

{'X':0,'Y':0,'dH':1.0}
{'X':1,'Y':0,'dH':1.1}
{'X':0,'Y':1,'dH':1.2}
{'X':1,'Y':1,'dH':1.3}


How to do this in a pythonic way?

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