I've just purchased an arm band type blood pressure meter which
relies on a stethoscope for taking readings.

With it the onset of sound made upon the initial rush of blood
is easy to hear and a reading of the systolic pressure is
easily gotten.

Where I have problems, is determining the diastolic reading.

The sound heard seems to drop in frequency, no longer rushing
but thumping, eventually disappearing..  It's hard to say
what's happening and the readings could be off by as much as 10-20
points.

What can I do to improve my readings ?

My present stethoscope is a cheaply made model.  Should I purchase
an expensive one ??

Thanks for your help..

liaM