It is strongly recommended not to measure the oscillator frequency directly at the crystal pins. The capacitance at the crystal pins is in the range of 10 pF, and the impedance on this signal line is several megaohms. A typical passive probe has a capacitance in the range of 10 pF and an input impedance of about 10 MΩ. Both values are in the range of the oscillator characteristics and heavily influence the behavior of the crystal oscillators. The MSP430 internal digital ACLK clock signal always carries the clock signal of the 32-kHz crystal oscillator. All MSP430 devices have the capability to output ALCK at one of the I/O pins. Measuring at this digital ACLK output does not influence the crystal oscillator in any way. ACLK still gives all necessary information to determine the stability and performance of the setup.