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The process of load cell calibration can be defined as a set of operations carried out under specified conditions to compare the output of the load cell to the value indicated in its datasheet, where both output values have a certain degree of uncertainty1.Basically a load cell calibration process can be carried through either of the following methods2Using a platform scale load frame and a set of calibration masses for applying compressive load forces or a hanging set of calibration masses to apply tensile load forces.Using a universal testing machine.By using the platform scale load frame method, it involves the use of some apparatus such as the load cell, signal conditioner, read out system, a loading apparatus, a hanger and calibration masses. The calibration masses comes in a set and increments of approximately 20, 40, 60, 80 and 100 percent of the rated capacity of the load cell. So in reply to the question asked, a load cell is not always calibrated using half of the maximum load, but by using sets of masses up to the maximum load. The figure below shows a set of calibration weights.The procedures for the above discussed method are:Power up all the electronic components about 30 minutes before the test.Connect the load cell to the signal conditionerEnsure a zero load on the load cell and also adjust the signal conditioner to 0 volts DC.Carefully place the load cell on a platform scale and place a scale beam on its load application point, ensure to tare its mass so the scale is balanced.Carefully place sufficient mass on the scale beam to equal 100% of the load cell’s rated capacity. Record the rated capacity value. The output of the signal conditioner should read ±10 Volts DCGently remove the mass from the scale and ensure the load cell is completely unloaded. The signal conditioner should read 0.00 Volts DC.Calculate the calibration mass requirements by obtaining the values of 20, 40, 60, 80 and 100 percent of the rated capacityPlace sufficient mass on the scale beam equal to 20% of the rated capacity and record the voltage output.Repeat the above step (8) for load increments of 40, 60, 80 and 100 percent pf the rated capacity of the load cellAlso unload the load cell by removing the mass corresponding to 80, 60, 40, 20 and 0 percent of the rated capacity. Also record the load decrements and the corresponding load cell voltage output.Repeat the loading and unloading process again to obtain two sets of readings.Sources:Digital Load Cells: A Comparative Review of Performance and Application, published 2003 by the Institute Of Measurement and Control, WP0803.United States Department of the Interior Bureau of Reclamation, USBR 1045-89, "Procedure for Calibrating Force Transducers (Load Cells)".The Essential Guide to Load CellsCell Calibration

The feds are already responding to the California drought, but not within the framework posed in the question details, which is ill informed.The federal government operates the Central Valley Project, a vast system of reservoirs and canals run by the US Bureau of Reclamation (Department of Interior). The main federal reservoir is Lake Shasta on the Sacramento River. The bureau manages water in coordination with the state operated State Water Project, whose main reservoir is Lake Oroville on the Feather River. River managment agencies in California are not competitive.There are other federal dams in California and throughout the west. If federal dams were built for flood control primarily, they are likely adminstered by the Corps of Engineers, US Army. If they were built for power and irrigation, primarily, they are run by the USBR. All dams are essentially multiple use dams, juggling hydropower, flood control, in-stream use and irrigation water storage.Other dam operators include municipal water districts and electric utility companies or districts.The Central Valley Project is enabled by law to serve as the manager of the river because it controls the river's flow. Even though it delivers water to those with entitlement rights, it can reduce the amount of those deliveries (but not change the priority of right). And it has done just that for two years running, reducing allocations to well below the full entitled rights and telling those with no entitlements, you aren't getting any federal water at all.This is a very big deal.The primary response of agriculture to water restrictions is to fallow fields and drill wells. Farmers are already pretty efficient in how they use water, given the nature of a crop and the economics of irrigating it. And the management of the river to maintain the avialability of water for all uses depends on the return flow to the river from irrigated fields. Plus, the replenishment of aquifers depleted by groundwater pumping depends on agricultural water seeping into the ground.The federal government isn't going to get involved with a general program of desalination because the economics of this option are essentially local. It may, however, grant money to planning programs that that are well thought out.A big opportunity for a new federal initiative would be the rethinking of federal levies protecting river flood plains. Such a rethinking has often been recommended but greatly resisted by local interests that are building suburbs and big box stores upon those flood plains. The most water efficent use of a flood plain would be to let it flood, thus recharging the aquifer and storing water that otherwise would be channeled by the levies out to sea. This is a great idea that will not likely come to pass until a thousand year flood makes the levies irrelevant.It is important to remember that snow and rain will still fall upon California. The amounts will be less than what water users have taken for granted. This is what a drought really means, an excess of demand over supply.

Hydraulic conductivities (K) can be obtained from pumping and slug tests as well as grain size analysis. Although empirical methods for such estimations are longstanding, there is still insufficient comparison of K values among the various approaches. Six grain-size analysis methods were tested on coarse-grained alluvial sediments from 12 water wells in NE Slovenia. Values of K from grainsize methods were compared to those of pumping tests and slug tests. Six grain-size methods (USBR, Slichter, Hazen, Beyer, Kozeny-Carman, and Terzaghi) were used for comparison with the Theis and Neuman pumping test method and the Bouwer-Rice method for slug tests. The results show that the USBR (US Bureau of Reclamation) method overestimates K values and there is no correlation with other results, so its use is not advised. Conversely, whilst the Slichter method gives much lower estimates of K, it is the only one to completely fulfill the grain size requirements. Other methods (Hazen, Beyer, Kozeny- Carman, and Terzaghi) result in intermediate values and are similar to the Slichter method; however they should be used for smaller-sized sediments. Due to their high transmissivity and small radius of inffiuence, slug tests should be avoided in the analysis of gravels, as they only test a small portion of the aquifer compared to pumping tests. This is confirmed by the low correlation coefficients between hydraulic conductivities obtained from pumping tests and slug tests.