From the DS2000A user manual, page 6-19 :
Press ? Measure->Counter to select CH1, CH2 or any channel of D0-D15 as the measurement source.
Besides, the signal input from the [EXT TRIG] connector can also be used as measurement source.
I couldn't find anywhere in the UI that would let you select EXT TRIG as the counter source
Not a problem I tought, I'll just use SCPI because...
DS2000A Programmers manual, page 2-143 :
:MEASure:COUNter:SOURce
Syntax
:MEASure:COUNter:SOURce <sour>
:MEASure:COUNter:SOURce?
Description
Set or query the measurement source of the frequency counter or disable the frequency counter measurement.
Parameter
Return Format
The query returns D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14, D15, CHAN1, CHAN2, EXT or OFF.
But selecting EXT as a source does nothing, the measurement is always 9.9e37 (which means no signal) and querying the source returns the previous source (chan1, chan2 or off).
Is there a way to use the EXT TRIG as a counter source as mentionned in both manuals?