I'm a pretty new emt (certified about a month now) and i just purchased the ADC 603 since it had good reviews and was alot less than a littmann. I am a little confused with the different heads and functions. The manual talks about high and low frequency sounds but doesn't say which sounds are high vs low (i.e. is BP high or low, how about lung sounds). I'm also confused with when to use the diaphragm (big side) vs when to use the bell (smaller side). Any help would be greatly appreciated and sorry if it's a really stupid question, my EMT course covered stethoscopes, BP, and lung sounds in about 20 minutes.