1.2E-4

The notation "1.2E-4" represents a number written in scientific notation. 

In this notation, the letter "E" represents "times ten raised to the power of." So, "1.2E-4" means 1.2 times 10 raised to the power of -4.

Mathematically, it's calculated as follows:

1.2 × 10^(-4) = 0.00012

Therefore, 1.2E-4 is equal to 0.00012. 

This is a common way to express very small numbers in a concise and readable format, especially in scientific and engineering contexts.