Tuning the 400 Probe

The standard Auto Switchable 4-nucleus probe (¹³C/³¹P/¹H/¹⁹F) is not tunable.

The inverse ¹H/X probe is tunable.

Why would you want to tune the probe?
1) You want to detect a nucleus other than proton or ¹³C.
2) If the probe is not tuned to your sample, the pulse width for full excitation will be longer than standard. The sensitivity will thus be less. Even if the pulse width for full excitation were calibrated, the sensitivity will be less.