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68 <strong>HID</strong> <strong>Sensor</strong> <strong>Usage</strong>s<br />
o Meters can be expressed as Unit(centimeter) with UnitExponent(0x02)<br />
Millibars, Bars<br />
o Millibars can be expressed as Unit(Pascals) with UnitExponent(0x02)<br />
o Bars can be expressed as Unit(Pascals) with UnitExponent(0x05)<br />
Knots (Knot = 1852 m / 3600 s)<br />
G’s (G = 9.8 m/s²)<br />
Millisecond<br />
o Milliseconds can be expressed as Unit(second) with UnitExponent(0x0D)<br />
Milligauss<br />
o Milligauss can be expressed as Unit(gauss) with UnitExponent(0x0D)<br />
In such cases, it is better for the default Unit of Measure to be one of these few above, and override it if<br />
necessary to a Unit of Measure for which there is a <strong>HID</strong>-expressible Unit().<br />
3.10 <strong>HID</strong> Unit Exponents<br />
Unit Exponents can be used to scale the numeric value of a Report Item by a power of ten according to the<br />
following table:<br />
Unit Exponent<br />
Argument<br />
Power of Ten<br />
(Scientific<br />
Notation)<br />
Power of Ten<br />
(Decimal<br />
Notation)<br />
0x00 1 × 10E0 1<br />
0x01 1 × 10E1 10<br />
0x02 1 × 10E2 100<br />
0x03 1 × 10E3 1 000<br />
0x04 1 × 10E4 10 000<br />
0x05 1 × 10E5 100 000<br />
0x06 1 × 10E6 1 000 000<br />
0x07 1 × 10E7 10 000 000<br />
0x08 1 × 10E-8 0.00 000 001<br />
0x09 1 × 10E-7 0.0 000 001<br />
0x0A 1 × 10E-6 0.000 001<br />
0x0B 1 × 10E-5 0.00 001<br />
0x0C 1 × 10E-4 0.0 001<br />
0x0D 1 × 10E-3 0.001<br />
0x0E 1 × 10E-2 0.01<br />
0x0F 1 × 10E-1 0.1<br />
Table 17. <strong>HID</strong> Unit Exponent encoding and meanings<br />
A Report Item that has a default Unit of Measure can be combined with a <strong>HID</strong> Unit Exponent to scale the<br />
Unit of Measure by a power of ten. Likewise, explicit Units of Measure declared with a Unit()<br />
descriptor item can be also combined with <strong>HID</strong> Unit Exponents to scale the Unit of Measure by a power of<br />
ten. For example:<br />
Unit(Second) with UnitExponent(0x0D) gives Unit(Milliseconds),<br />
Unit(gram) with UnitExponent(0x03) gives Unit(kilogram),<br />
Unit(Centimeter) with UnitExponent(0x02) gives Unit(Meter).<br />
See Also<br />
For more information about <strong>HID</strong> Unit Exponents; please refer to Section 6.2.2.7 of the Device Class
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