Excel Terminology

A serial date number is an integer that represents the date in the Excel calendar.  By default, day 1 is January 1, 1900, through to 2,958,465 representing December 31, 9999.

Storing dates using serial date numbers dramatically simplifies the calculation of durations and dates into the future and past as simple integer arithmetic.  Number formatting takes care of displaying the numbers as a date for user readability.

The actual numbers and date range may change based on the date setting in the workbook..

A serial time number is a decimal value that represents the time of day or elapsed time in Excel.  As a time of day value, the value 0 represents 0:00am (midnight) and the value 0.999988425925926 represents 23:59:59 (11:59:59 PM).  For elapsed time, the value represents the multiples of 24 hour periods elapsed.  12 hours is .5, 24 hours is 1, 36 hours is 1.5 and so on.

Storing times using serial time numbers dramatically simplifies the calculation of durations and times of day into the future and past as simple decimal arithmetic.  Number formatting takes care of displaying the numbers as a time of day or time elapsed.  By default time formats display the time value of the decimal portion only.  Special formatting is required to show elapsed times above 24 hours - placing brackets around the hours portion of the format..

The String Prefix character is the apostrophe (').  When prefixed to a value entered into an Excel cell, it signals to the system to store that value as a text string, regardless of whether it looks like a formula or another intrinsic value.  No interpretation of the value is undertaken and the formula is stored as 'entered characters.  The value in the cell is a text string consisting of the charcaters only and not including the string prefix character.

The term "Sum of Comparison" is used on this site to describe the substitution of an expression that sums the results of two or more comparison operations to apply a logical OR to a set of values.  Since the OR function cannot be used in an array expression, except where all conditions are to be evaluated at once, the use of a sum of two or more comparisons enables evaluation cell-by-cell of logical OR conditions thus: (A1:A10>10)+(B1:B10<10)>0 will return TRUE for each of the ten rows if either or both conditions are met.