I had someone ask me what specific gravity (Relative density or g/l or ppm) was and asked me to explain it so it took me about a half hour to explain it fully and the person who asked me look like a monkey with a math problem after I was done lol

anyway to explain SG you have to under stand what extactly are we reading
CONCENTRATIONS
1 milligram/Liter =1 ppm (part per million)
1 microgram/Liter =1 ppb (part per billion)
1 nanogram/Liter =1 ppt (part per trillion)
Conversion factors and comparisons of units
Most of the chemical data that is reported for waterbodies is expressed as a concentration: a mass of chemical per unit volume of water. Most of the total dissolved solids content of ordinary water consists of common salts with the predominant ions being calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride and silicate. These ions collectively are usually in the range of about 20 to 1000 mg/L (milligrams per liter) - the low end being very soft water and the high end being very hard (high in minerals -
usually calcium and magnesium carbonates).
A milligram per liter of water is equivalent to 1 ppm (part-per-million) because a liter of water weighs 1000 grams and a milligram is 1 one thousandth of a gram.
The various forms of nitrogen and phosphorus most available to plants (nitrate-N, ammonium-N and phosphate-P) are typically present at concentrations or levels of only 0.001 to 0.500 mg/L . These are typically expressed as micrograms-per-liter or ug/L . A microgram /L is 1 one thousandth of a milligram/L . It is also equivalent to 1 ppb (part-per-billion).
Toxic pollutants such as heavy metals like cadmium and mercury usually exist at sub - ppb levels and can be considered to be a problem at ppb levels. Some organic contaminants, a diverse group of chemicals that includes pesticides, PCBs and dioxins, may be measured at sub- ppb levels and may be expressed as ng/L (nanograms-per-liter = parts-per-trillion) or even 1 pg/L (picograms- per-liter = parts-per-quadrillion).
Seawater has a salt content of about 32 g/L (32 parts-per-thousand which is the same as 3.2 % since 1 percent = 1 part-per-hundred). This is also equivalent to 32,000 ppm (part-per-million) and on most refractometers is expressed as 32 PPt (part-per-thosand I really don't know why they use it because anyone else woud read that as part-per-trillion PPT.....confusing lol) . which is 1.025SG which well all know we are looking for
SG
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water. The term "relative density" is often preferred in modern scientific usage.
If a substance's relative density is less than one then it is less dense than the reference; if greater than one then it is denser than the reference. If the relative density is exactly one then the densities are equal; that is, equal volumes of the two substances have the same mass. If the reference material is water then a substance with a relative density (or specific gravity) less than one will float in water. For example, an ice cube, with a relative density of about 0.91, will float. A substance with a relative density greater than one will sink.
Specific Gravity = object in air weight/equal volume of water weight (both parts of the equation are expressed in either Newtons,dyane,pound force,kilogram force ( which are all a measurement of force I wont go into the conversion from one to another)
Fun facts
One-Part-Per-Million
one automobile in bumper-to-bumper traffic from Cleveland to San Francisco
one inch in 16 miles
one minute in two years
one ounce in 32 tons
one cent in $10,000
One-Part-Per-Billion
one 4-inch hamburger in a chain of hamburgers circling the earth at the equator 2.5 times
one silver dollar in a roll of silver dollars stretching from Detroit to Salt Lake City
one kernel of corn in a 45-foot high, 16-foot diameter silo
one sheet in a roll of toilet paper stretching from New York to London
one second of time in 32 years
One-Part-Per-Trillion
one square foot of floor tile on a kitchen floor the size of Indiana
one drop of detergent in enough dishwater to fill a string of railroad tank cars ten miles long
one square inch in 250 square miles
one mile on a 2-month journey at the speed of light
thanks for reading guy/gals you get a "A" if you understand what i was saying