The indicator graph dose not go down to minimum

The indicator graph dose not go down to minimum even if the cpu is at the lowest frequency.

My cpu is Intel(R) Core(TM)2 Duo CPU E8400

Output from cpufreq-info:

driver: acpi-cpufreq
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 10.0 us.
  hardware limits: 2.00 GHz - 3.00 GHz
  available frequency steps: 3.00 GHz, 2.67 GHz, 2.33 GHz, 2.00 GHz
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance
  current policy: frequency should be within 2.00 GHz and 3.00 GHz.
                  The governor "ondemand" may decide which speed to use
                  within this range.
  current CPU frequency is 2.00 GHz.
  cpufreq stats: 3.00 GHz:23.78%, 2.67 GHz:1.72%, 2.33 GHz:1.82%, 2.00 GHz:72.68% (2226)