Fluid Flow out of a Liquor Bottle

[d_v]

I was working on a project for which I was considering letting a liquid flow out of a bottle rather than pump it out, but I know that the flow rate changes as the height of the fluid within the container changes, which is an issue. I then remembered that bartenders count time to measure their pours. I can't see any way this is remains accurate as the bottle becomes more empty. I could only imagine that they make small, unconscious adjustments as this happens.

Can anyone see any way that the flow rate may remain constant out of a liquor bottle for varying heights of the liquor?
(I found this page to be a good resource: http://www.engineeringtoolbox.com/bernouilli-equation-d_183.html)

 

[Simon Bridge]

Welcome to PF;
Good observation. You should get a bottle, any old bottle, and upend it and see what happens.

Note:
Bar bottles usually have a special nozzle
poured measures are not very accurate even if the bartender is counting time.
(Ask yourself - how accurate does it need to be?)

A fluid may flow at a constant rate out a hole if there is something else restricting the flow.
Consider - there is the weight of the liquid above the hole, the air pressure, and the viscosity of the fluid.
The flow is likely to be uneven if the air has to push its way through the liquid to get into the bottle ... if the air cannot get into the bottle, the flow will slow and stop.

 

[SteamKing]

And remember, you are in a bar, not a lab, where different protocols are supposed to apply.