Excel Interpolation in MATLAB function

Hi, I am writing a code that is supposed to read values from excel table, the table consists of 2 columns temperature and viscosity. The user should enter the the temperature and the code returns the corresponding viscosity. and if the temperature is not in the table, the code should interpolate to get the corresponding viscosity. So far I managed to do the first part(that if the temperature is in the table the code returns the viscosity).But I am having difficulty in the interpolation part. For example if the user enters temperature=27 the result will be 0.000855,

 but if the user enters temperature=30 the code will not work.
Hope I made myself clear.

function b = watermiu(a)
data = xlsread('water temp miu.xlsx');
index = data(:,1) == a;
b = data(index,2);

Answer 1

[Image Analyst]

You might try splines. See attached demo and adapt as needed.