## 4 Discussion  
Changes in needle diameters and dripping speeds affect the diameter of generated drops. Generally, a reduction in the needle diameter leads to decreasing drop diameters. Drop diameters d 10 and d Max are important as lower and upper drop diameter limits for every needle. The largest measured d Max of 3.69 mm is generated using a 16G needle at a dripping speed of 360 drops\(\cdot\)min\({}^{-1}\), while the lowest d 10 of 1.42 mm is generated using a 32G needle at a dripping speed of 10 drops\(\cdot\)min\({}^{-1}\). In the case of 16G and 18G needles, d Max is determined by the proposed speed limit for counting drops of the DCLS, 360 drops/min. In the case of smaller drops (19-32G needles), d Max is achieved at a lower  
Figure 4: For different drop sizes. this figure shows (**a**) the height the drops need to fall to achieve 50%, 75%, 90%, 95%, or 99% of the terminal velocity of fall, (**b**) the velocity at that height, and (**c**) the kinetic energy of the drops at that height. Note: this does not depend on whether the drop sizes are measured, interpolated, or extrapolated. It just depends on the drop diameter. dripping speed, after which the dripping diameter gradually decreases with the increase in the dripping speed. The measurement of water pressure shows that to start dripping requires some pressure in the hydraulic system. The lowest observed pressure h 10 is 14 mm of a water head for a 16G needle and was recorded at a dripping speed of 10 drops\(\cdot\)min\({}^{-1}\). A gradually rising water pressure increases the dripping frequency too. The water pressure h 10 is drastically enlarged in a 30G needle compared to 16-27G needles. However, since the maximum pressure allowed on a pressure gauge is 1970 mm (Figure 2b), we conducted measurements of pressure for a 30G needle until reaching the pressure gauge maximum scale reading and estimate further pressure by assuming linear relation. For a 32G needle, measurements of water pressure are not possible because the PG exceeds the upper scale limit of 1970 mm in the pressure gauge. We can clearly observe that with the rising water pressure, the dripping speed in the hydraulic system also increases, following a linear regression curve (Table 3). However, it is important to note that, given the non-uniform length of all needles, the length will affect water flow resistance too. Therefore, the drop diameter and water pressure relations to dripping speed could also be affected, especially for 27G to 34G needles (for an OD Nom of 0.40 mm to 0.18 mm)  
Both power and logarithmic regressions provided excellent relations of d Avr vs. OD Nom All (Figure 3). However, it is necessary to emphasize that there are possibly slight deviations in those relations due to different needle OD and wall thickness deviations within proposed tolerance values (Table 1). Based on the d vs. OD Nom All distribution, we can observe that the power regression would potentially overestimate the drop diameters generated by needles. On the other hand, logarithmic regression would potentially underestimate the drop diameters (Figure 3). However, drippers from [30] represent metal needles and tubes (with sharp and obsolete tips, respectively), which may not necessarily correspond to the dripper diameters proposed by the ISO 9626:2014(E) international standard. Nonetheless, all regressions are in accordance with findings from [39], which report that an increasing dripper diameter impacts the detached drop weight, i.e., drop diameter, and becomes less dependent on the dripper diameter. The size of natural raindrops ranges from 0.12 to 7.00 mm [40], although it rarely exceeds 4 mm [41; 42; 43; 44]. Therefore, it is possible to generate these drops using needles as drippers (Figure 3). As [31] suggested, the significance of being able to produce 5 mm drops under controlled conditions becomes apparent when the criteria proposed by [45] are considered.