How to calibrate a spreader or sprayer

You can opt to spread in one pass or two overlapping passes at half the rate. Two passes is likely to give a  better result. Either way you will need to calibrate the spreader accordingly.
The Ev-N-Spred 2050P spreader has a numerical scale, the setting is dependent on the granule size and density. The fertilisers that I supply are virtually all the same consistency so once you have calibrated the spreader you won't have to change it again. I use a setting of 10.5 on the scale provided. This delivers about 15 to 16 gsm and I always do a double pass so the toatal amount applied is 30 to 32 gsm.. You may need to make small adjustments because your walking speed may differ from mine. 
For other spreaders you will need to calibrate the spreader.  Here are two ways to calibrate - I have tried both but prefer the second - the lazy way!
The scientific way.
To calibrate you need a length of polythene or tarpaulin about 4 metres by 10 or 15 metres. A 10 metre tape measure. A set of hanging scales and bucket. 
1/. Weigh 5kg of fertiliser into bucket. 
2/, Pull lever on and walk at normal speed for 10 metres over polythene then immediately switch off. 
3/. Tip remaining fertiliser from spreader into bucket and weigh to establish how much fertiliser has be used. 
4/. Measure spread width.
5/. Calculate application rate: Weight used divided by area covered (Spread width x 10 metres). So if 500 grammes was used and the spread width was 10 metres the result would be 500 divided by 30 = 16.67 gsm. You want a rate of 16 gsm so adjust the lever setting accordingly. You can then re-run the test at the new setting. When you have finished you can retrieve the fertiliser from the polythene.
The lazy way 
Weigh  5kg of fertiliser into a bucket and pour into the hopper. With a setting well below medium walk the spreader the length of one lawn and get an assistant to measure the spread width. Now calculate the area covered. This is 32 metres (the length of one lawn) x the spread width. If the spread width was 3 metres, the area covered is 32 x 3 = 96 sqm. Tip out the remaining fertiliser from the hopper into the bucket and weigh again to see how much was used. If 2kg was used the application rate was 2000 grammes divided by 96 sqm = 20.83 gsm. Adjust the setting on the spreader accordingly and repeat the process but move one spread width across the lawn so that you don't double dose the lawn. Very soon you will have arrived at the correct setting and shouldn't have to make further changes. You may end up with a slightly uneven application where you started but if you approach this with a cautious setting to begin with no harm will be done.
I find this is the easiest way and is more accurate than the scientific way because the area covered is so much larger.
Calibrating the Brilliant Broadcast Sprayer 
You need to judge your speed so that the tank runs dry at the right time. The correct speed is about 32 yards per minute. I recommend that you test this with water first.    
Bout markers
To apply accurately you should use bout markers. These can be anything from bamboo canes to flower pots. I use electric fence posts which have sharp spikes and are easy to use. They are available online for about £10 for ten. At croquet clubs it is a good idea to have permanent bout markers, these can be painted on boundary boards (see the picture). The markers are set 3 metres apart for the Earthway 2050P spreader and 4 yards for the Brilliant Sprayer.
Spreading with an Earthway 2050P
With a spreader, the first pass is marker to marker and the second pass is gap to gap which ensures an even overlap.  Then spread the 3 metre wide strips at the North and South boundaries. For the second pass repeat the process but instead of going gap to gap, you go marker to marker thus overlapping the previous application. Spread the 3 metre strips at the North and South and you will be left with two 1.5 metre strips down the East and West boundaries. Set the 2050P shut off lever so that it spreads half width and apply to those strips. 

First pass - Spraying or Spreading

Second pass - Spraying or spreading

Spraying with a Brilliant Sprayer
This sprayer has a 4.6 yard spray width. To allow for feathering at the extremes, it is best to spray on the basis of a 4 yard width. The spraying can be single pass as shown below or double pass if you tow faster. To spray 50 litres per lawn allow 9 to 12 minutes of spray time depending on your preferred pattern. First spray up and down the lawn, leaving a 4 yard strip at the North and South boundaries, then spray those boundary strips.

Ev-N-Spred 2050P

Ev-N-Spred 2050P setting scale.

Bout markers painted onto boundary boards