In what situations should developers avoid using units of measurement in PHP calculations to prevent errors or unexpected results?

When performing calculations in PHP, developers should avoid mixing units of measurement (e.g., mixing inches with centimeters) to prevent errors or unexpected results. To ensure accurate calculations, it's important to convert all units to a consistent measurement system before performing any arithmetic operations.

// Example of converting inches to centimeters before performing a calculation
$inches = 10;
$centimeters_per_inch = 2.54;

$centimeters = $inches * $centimeters_per_inch;

echo $centimeters;