"Toppers" wrote...
=COUNTIF(A2:A1000,""&B2)-COUNTIF(A2:A1000,""&C2)

B2=401, B3=501 etc
C2=500, C3=600 etc
....

Classic mistake. Note that the OP's VERY FIRST data point was 500.6.
However, using your intervals above, the formula for the next range using
your formula above would be

=COUNTIF(A2:A1000,""&B3)-COUNTIF(A2:A1000,""&C3)

which would be equivalent to

=COUNTIF(A2:A1000,"501")-COUNTIF(A2:A1000,"600")

So both your original formula and my extension of it to the next interval
would skip the value 500.6. It would have been safer to use just one set of
bounds

B2: 400
B3: 500
B4: 600

and formulas like

=COUNTIF(DATA,""&B2)-COUNTIF(DATA,""&B3)

=COUNTIF(DATA,""&B3)-COUNTIF(DATA,""&B4)

The second of these would include 500.6 in its count. I really doubt the OP
would have wanted to exclude data points for which 0 < MOD(x,100) < 1.