Yeah, DC ratio of a stable signal. If the signal varies, it's usually due to thermally related shifts in a current sense shunt resistor or in my equipment. Things are usually pretty settled after 30 minutes.
Although below say 0.25V, I wish I had a more stable voltage source than my ITECH IT6123B. That thing is super nice in terms of being within 1mV across its range, typically, but at low voltages, even 100µV of drift matters.
Oh, perhaps I should have said: I thought to write this post while taking that measurement with 250mV and then 125mV input to hit a certain range on an amplifier. I could see the signal drifting during the long term average, hence my thought to synchronize the meters. Maybe I just need a more stable source for low voltages.