As is known in the art, there are certain medical conditions which, if not treated, can lead to severe dehydration and death.  Cholera is one example of such a medical condition.  To treat cholera and other conditions, an intravenous (IV) drip infusion is often used to re-hydrate patients and/or to introduce medicine into a patient's body.  An intravenous drip infusion of saline is the preferred technique for the medical treatment of severe cholera.  In a cholera epidemic, where many patients need to be treated as quickly as possible, it is desirable set up IV equipment and initiate treatment as rapidly as possible. 
As is also known in the art, a conventional IV drip set includes a fluid reservoir, a clear plastic drip chamber coupled to the fluid reservoir for visualization of fluid flow, a clear flexible tube coupled to the drip chamber, a roller clamp coupled to the flexible tube for flow rate control, and an attachment to connect the flexible tube to an intravenous catheter adapted to be placed into a patient.  The roller clamp provides an adjustable force upon the flexible tube and therefore an adjustable flow restriction.  The rate at which fluid flows through the tube is estimated by observing the drip rate in the drip chamber.  The rate at which the fluid flows through the tube is adjusted by adjusting the roller clamp until the desired drip rate is achieved.  Such conventional IV drip sets are simple, relatively inexpensive and find widespread use.  One example of a conventional IV drip set is further described in conjunction with FIG.  1 below. 
When using the IV drip set, it is important for the user to accurately regulate the flow of fluid (e.g. saline solution) into the patient.  The roller clamp is used to adjust the flow rate of the fluid flowing through the flexible tube and therefore the flow rate into the catheter, which is inserted into the patient's body.  A user turns an adjustment roller on the roller clamp to provide more or less force, or clamping action, upon the flexible tube and therefore more or less restriction of the flexible tube, thereby adjustably controlling the flow rate. 
It is relatively difficult for a user to accurately adjust conventional roller clamps to accurately provide a specific flow rate.  Thus, to arrive at a specific flow rate, it is often necessary to make an adjustment, observe the resultant flow rate via the drip chamber, and then re-adjust as necessary.  These steps are repeated until arriving at a desired specific flow rate.  Flow rate adjustment can, therefore, be a relatively time-consuming task. 
The difficulty in adjusting the flow rate is due in part to a large non-linearity in flow rate control provided by conventional roller clamps.  Essentially, as the user turns the adjustment roller of the conventional roller clamp, the flow rate is not linearly adjusted in proportion to the rotation of the adjustment roller.  The non-linearity is sufficiently great that even a slight rotation of the adjustment roller in either direction can cause an undesired flow rate either higher or lower than the desired flow rate.  Furthermore, with each adjustment of the adjustment roller, the drip rate in the drip chamber must be observed to determine the flow rate.  Observation of the drip rate involves counting a number of drips over a time period, for example, 15 seconds.  As described above, particularly in epidemic situations, it is necessary that set up of the IV drip set, including adjustment of the flow rate, be done quickly.  Difficulty of flow rate adjustment slows the set up process. 
Therefore, it would be desirable to provide a flow rate measurement apparatus that quickly indicates the flow rate of the IV drip set, without counting drips of a period of time.