nPoints=10000;

Experiment 1 : X = A - B

results1={};
Do[
A=N[RandomInteger[{-5,5}]/10+1];
B=N[RandomInteger[{-5,5}]/10+1];
X=A-B;
AppendTo[results1,X];
,{i,1,nPoints}];

plot1=Histogram[results1,{-1,1, 0.1}]

Experiment 2 : X = A - B + C + D

results2={};
Do[
A=N[RandomInteger[{-5,5}]/10+1];
B=N[RandomInteger[{-5,5}]/10+1];
cC=N[RandomInteger[{-5,5}]/100+0.1];
dD=N[RandomInteger[{-5,5}]/1000+0.01];
X=A-B+cC+dD;
AppendTo[results2,X];
,{i,1,nPoints}];

plot2A=Histogram[results2,{-1,1, 0.1}]
plot2B=Histogram[results2,{-0.01,0.01, 0.001}]