Degree Sign. The degree sign () is usually included in expressions of temperature, although not in references to the kelvin scale (e.g., 2 000 K). There is no space left between the degree sign and the abbreviation F, C, or R (e.g., 100F, 32C, or 491.67R).
Percent Sign. Percentages are written as a figure followed by an unspaced percent (%) symbol. The sign is included with all numerals in a series or range, even if one of the numbers is zero (e.g., rates of 8.3%, 8.8%, and 9.1%; a variation of 0% to 10%, or a 0%10% variation*). The symbol is not substituted for the word "percent" without an accompanying number (e.g., a small percent of the test plants).
*In text, it is preferable to denote the range using the word to. The construction using the en dash may be used in tables and figure callouts if space is limited.
Coefficient and Variable. There should be no space between a coefficient and a variable (e.g., 4sy not 4 sy).
Units of Measure. Units of measure are separated from quantity by one unit space (14 in., 12 kg).
Operational Signs. Operational signs (+, , =, x) are separated by one unit space:
2x2 6x 5 = 0; 10F ± 5F. The exceptions to this rule are as follows:
thin space around a slash used to denote a division sign ( / ).
EXAMPLE: kl / r > CC
no space between +, , ± and quantity when it indicates measure
EXAMPLES: 15%, ±3
thin space between square root symbol and preceding math.