♻ PLASTIC BOTTLE RAIN GAUGE ♻

This is a simple rain gauge made from a plastic bottle. My father tought me how to do it.
We always use it for deciding if and when we should water our fruit trees. (keep in mind that on a hot summer day 4 or 5 mm of water a day evaporated from the ground, so if it rained 50 mm, you don't need to water your trees for about 10/12 days).

MATERIALS:
_plastic bottle (conic or funnel shaped);
_strong tape;
_stick or cane.
TOOLS:
_cutter;
_permanent marker;
_scales or capacity measure for liquids;
_ruler.

remove labels  with warm water, and cut away the bottom of the bottle with cutter.

_measure the open AREA of the bottle opening:  r • r • 3.14 (measure the diameter, divided it in 2 and find the radius, then 
      do  radius by radius by 3.14);
_now, knowing that if it rain 1l of water on 1 square meter it will correspond at 1 mm of water, we need to find out how many ml in your bottle that mm of rain fall on the ground will correspond  (x).  We need to use this formula:
 
      1m²           bottle open area                                    1liter   •  bottle open area
     --------   =    ---------------------               so:            x= ----------------------------------
     1 liter                    x                                                                 1m²

this is an example using the measurement of my bottle, my bottle diameter was 8.6 cm ( than 4.3 cm of radius)
4.3cm•4.3cm•3.14=58cm²                ( 58cm²=0.0058m²)

      1m²           0.0058m²                                            1 liter • 0.0058 m²
     ---------  = ------------------                   so:           x= ---------------------------         so:       x=5.8 ml
      1 liter               x                                                             1m²


another way to find your x  is: calculate the volume of 1 mm of water on the area of open surface of your water bottle, and use that number to make the measurements on your bottle:
r•r•3.14•0.1cm²=x    (than transform it: 1cm²=1ml)

now you have found x.    
_x is the corresponding measure on your bottle of 1 mm of rain fallen on the ground, so we need to use it to mark the measurement on the bottle.
_because the number you will find is so small I will multiplied it by 5 times (so it will correspond to 5 mm of rain fallen on the ground).
_pour in the bottle the milliliters of water you just measured (5x) and mark it with permanent marker (write 5 mm). you can use a capacity measure for liquids or a scales (1l of water weigh one kilo).
_keep adding milliliters and marking until you mark the whole bottle.


example of my bottle:
_my x were 5.8 ml  
_5.8 ml•5= 29 ml (corresponding at 5 mm of rain fallen on the ground)
_I signed the 5, 10, 15, 20,30,40,50,70,100 and 150 mm of rain on my bottle.
 

place the stick on the bottle (like in the photo) and stick it with tape.

you 're done! place the pluviometer (rain gauge) in your garden (stick the cane in the dirt), far from trees or roofs.
empty after every rain: you just need to unscrew the cap of the bottle.