To measure the area of an arbitrary two dimensional shape you will use a planimeter. To measure an area you could also just use a simple ruler depending on how big the area is.
1/2(bh)
Pi (3.141...) is used for circles, and circles only. You use it to find the area and circumfrence.
-- Find out the population of the area. -- Find out the area of the area. -- Divide the population by the area. The result is the population density of the area.
ruler
Spectrometer
the instrument that the used was an intelligent brain
The best place to find used drums sets may be online, or at a used instrument store. You can visit one in your area and perhaps get used drums sets for a cheap price.
A compass is used to find your location in a forest
A violin can be used, but its effectiveness is limited.
Graduated cylinder
Pressure gauges.
A scale
A Planimeter.
This instrument is called pluviometer (a rain gauge). See the link below.
radar
A set of scales
Scales.