I'm playing around with an REF5010 voltage reference, and its data sheet specifies an output capacitor with an ESR of 1 to 1.5Ω for best performance. Now when I measure the ESR of electrolytic capacitors it varies widely depending on the frequency (I have an U1733C LCR-meter that can measure at 100Hz, 1kHz, 10kHz and 100kHz).
The Wikipeadia article on ESR says
If not otherwise specified, the ESR is always an AC resistance measured with standardized frequencies.
but fails to provide details.
Which frequency (maybe depending on circumstances?) is used for determining the ESR of capacitors?