When you provide a numerical array to find, it gives the indices of all the nonzero values. And as Max_floor_2 is a non-zero scalar, it returns r=1, c=1.
Time=[0700:100:1800]';
Floors=[5,13,10,14,42,49,46,67,64,32,12,4
8,17,28,39,66,71,74,154,126,57,20,7
2,8,15,24,14,51,48,68,145,55,11,2]';
Readings=cat(2,Time,Floors);
If you want to obtain just the index of the 1st occurence of the maximum value (in case there are multiple maximum value present in the array), utilize the 2nd output of max
[Max_floor_1,idx1] = max(Readings(:,2))
In case, you want all the indices of occurence of maximum value, compare the maximum value to the array and then use find -
index = find(Readings(:,2)==Max_floor_1)
Also, it's not a good practice to dynamically name variables, read - TUTORIAL: Why Variables Should Not Be Named Dynamically
Take advantage of the functionalities -
[Max_floor,index]=max(Readings(:,2:4),[],1)
