Liquor pourers, often used in bars and restaurants, are designed to provide a consistent and controlled pour, but their accuracy can vary based on several factors. 
Standard pourers, like free-flow pourers, rely on the bartender's skill and timing to achieve the desired measurement, which can lead to inconsistencies. These pourers do not have built-in mechanisms to stop the flow at a specific volume, so accuracy depends on the user's ability to count or time the pour correctly.
Measured pourers, on the other hand, are designed to dispense a specific amount of liquid, such as 1 ounce or 1.5 ounces, before automatically stopping the flow. These are generally more accurate than free-flow pourers, as they have a built-in mechanism to control the volume. However, their accuracy can still be affected by factors such as the angle of the bottle, the speed of the pour, and the viscosity of the liquid.
Environmental factors, such as temperature and humidity, can also impact the performance of pourers. For instance, colder temperatures can increase the viscosity of the liquor, affecting the flow rate and potentially leading to under-pouring.
In summary, while measured pourers are generally more accurate than free-flow pourers, their precision can still be influenced by external factors and user technique. For the most accurate measurements, especially in professional settings, using a jigger or a digital measuring device is recommended.