Rain Gauge

A rain gauge / Udometer / Pluviometer / Ombrometer is a type of instrument used to gather and measure the amount of liquid precipitation over a set period of time.

Standard rain gauge

A standard rain gauge consists of a funnel emptying into a graduated cylinder of 2 cm in diameter, that fits inside a larger container of 20 cm in diameter and 50 cm in height.

When measurements are taken, the height of the water in the small cylinder is measured.  Excess water overflowed into the larger container is measured too to get a total rainfall. 

General practice is to examine the gauge daily; to measure the water, if any; and to enter the record at once.

Rain is measured in units of length per unit time, typically in millimeters per hour.  One millimeter of rainfall is the equivalent of one liter of water per square meter.

Other types of rain gauges :

1. Weighing precipitation gauge

2. Tipping bucket rain gauge

3. Optical rain gauge

4. Acoustic rain gauge

Raindrops

Raindrops have sizes ranging from 0.1mm – 0.9 mm diameter, above which they tend to break up.   The biggest raindrops ever recorded was 10 mm diameter.

	Drizzle Size : < 0.5 mm  velocity : 2 ms-1
	Cloud droplets size : 0.5-  2.0 mm shape : spherical
	Normal drain drops size : 2.0 – 5.0 mm shape : oblate
	Large drain drops size : > 5.0 mm shape : hamburger buns / parachutes velocity : 9 ms-1
Source : wikipedia	contrary to popular belief, raindrops does not resemble a teardrop.

Marker Pen

Paint markers are permanent markers used to write on a variety of surfaces, eg steel, rubber, timber, plastic, etc.  The  ink is an oil-based paint and generally requires shaking before use.

Permanent markers are porous pens used to writ on smooth surface such as glass, plastic, wood, metal and stone.
The ink comprises a main carrier solvent, a glyceride, a pyrrolidone, a resin and a colorant, making it waterproff.  The marks can be removed by acetone, xylene, toloune, isopropyl alcohol, or ethyl acetate.

Permanent marker was invented in 1952 by Sidney Rosenthal.

A Whiteboard marker is for temporary writing on slick, non-porous writing surface, eg. OHP, whiteboards, glass etc.

Whiteboard marker was invented  by Jerry Woolf of Techform Laboratories.  
It was later patented and produced by Pilot Pen in the 1960s.

Highlighters are permanent markers used to highlight and cover over existing writing while still leaving the writing readable.
A highlighter fluorescent colour is coloured by pyranine.

Highlighter was first introduced in 1963 by Carter's Ink Company.