It was taught back in the day that different location will sustain a pulse to feel by palpation a bit longer than other locations. Essentially it was carotid and femoral arteries and if I recall correctly 90 systolic could be considered the BP if pulse was felt in these locations. It wasn't an exact science and it was developed in a clinic setting and not at locations first responders would typically be trying to determine a blood pressure.
However, what was taught was to use sphygmomanometer and use palpation to determine BP. This is cut and past from the PJ medical protocols that was used back in the day:
"Because of aircraft noise and vibration, the measurement of blood pressure by auscultation with a stethoscope is virtually impossible. Therefore, systolic B.P. measurement must be accomplished by palpation of the brachial or radial artery."
This method worked some what satisfactorily when in a warm (room temperature) or warmer environments, but not to well as fingers get effected by a cold environment. One of the reasons I wasn't to happy with treating injured on the initial put in service H-60 helicopters is lack of heater to keep cabin warm.
This being said sphygmomanometer technology has improved in that listening for or palpating for a radial pulse is no longer required, but good circulation in at least one arm is still needed.