How does negative values occur in NIFTY?

[ritesh2000.sinha]

in nifty case study i didnt understand how the -ve values came i.e nifty.values[1:]-nifty.values[:-1] ==>in this code -ve values are coming and i dont understand how they subtract each other

what i did
s=nifty.values[1:]
t=nifty.values[:-1]

s[0]-t[0]//-117.0034 s[0]-t[1]//0

i cant understand how did the subtraction happen

[saag]

here the task seems to measure the change with respect to the previous closing. Hence the negative values highlight a negative change or a drop in the closing of the current day from its previous. Hope this helps!