# D3DDDI_RATIONAL structure

The D3DDDI_RATIONAL structure describes a fractional value that represents vertical and horizontal frequencies of a video mode (that is, vertical sync and horizontal sync).

## Syntax

```
typedef struct _D3DDDI_RATIONAL {
UINT Numerator;
UINT Denominator;
} D3DDDI_RATIONAL;

```

## Members

Numerator

[in] The numerator of the frequency fraction.

Denominator

[in] The denominator of the frequency fraction.

## Remarks

Vertical and horizontal frequencies are stored in Hertz (Hz). The dynamic range of this encoding format, given 10⁻⁷ resolution, is {0 to (2³² - 1) / 10⁷}. This range translates to {0 to 428.4967296} Hz for vertical and horizontal frequencies. This submicrosecond precision range is acceptable even for a provided application. (An error of one microsecond for video signal synchronization would imply a time drift with a cycle of 10⁷/(60 x 60 x 24) = 115.741 days.)

For a rational number with a finite fractional sequence, use a denominator of the form 10(length of fractional sequence). For a rational number without a finite fractional sequence, a sequence that exceeds the precision that the dynamic range of the denominator allows, or an irrational number, use an appropriate ratio of integers that best represents the value.

## Requirements

 Version Available in Windows Vista and later versions of the Windows operating systems. D3dukmdt.h (include D3dukmdt.h)