In a Math Toolbox equation, designating variables with a V, such as V123, means that a value must exist for it before the equation can calculate. An equation will not calculate if a value does not exist for every Vtype variable used in the equation. In such case, a blank will be printed in any of the reports for this calculation indicating that there was insufficient data to perform the calculation.
There is another method of designating a variable within an equation  as a conditional variable. When a variable is declared a conditional variable, it means that if no value presently exists for the variable, that term is ignored in the equation. If an equation can be solved adequately without a value for a certain variable, that variable should be designated with a C, such as C124.
Differences between addition using V variables and addition using C variables :
V1 
V2 
V1+V2 
C1+C2 
1 
2 
3 
3 
 
2 
 
2 
 
 
 
 
0 
2 
2 
2 
0 
0 
0 
0 
"" denotes a blank value
In summary, those variables essential to the calculation of an equation should be given a Vtype designation. Variables not essential to the calculation of the equation should be given a Ctype designation. When using variables in functions (i.e. WAVG, DDIF, ...) refer to help topic on the function to determine when to use a C or a V.
NOTES:

When multiplying, dividing, or raising a number by a Conditional reference where the value is blank, the value calculated will be blank and the equation will continue to be evaluated.

When adding or subtracting a Conditional reference to a number when the value is blank will return that number and the equation will continue to be evaluated.
Examples:
V1 
V2 
V1*C2 
V1*C2 
V1 * C2 +10 
1 
2 
2 
2 
12 
 
2 
 
 
 
 
 
 
 
 
1 
 
 
 
10 
0 
0 
0 
0 
10 
"" denotes a blank value
SEE ALSO: IF (Conditional statement), ISBLANK