Very flat frequency response from 4 hz to 2 mhz. After a few adjustments, my over 54 year old 209a was within .04 db over the entire range. Also very low distortion and within 50 nanosecond risetime on the square wave output. Frequency accuracy was generally within one dial division throughout. HP's best and most versatile low frequency generator. Better than the previous 204a and earlier models. Smart buyers know this and have bought most of the "used" supply. These are hard to find currently, and I was fortunate to locate one on Ebay for under $100- working!