The SI prefix "deci" represents a factor of
10^{-1}, or in exponential notation, 1E-1.

So 1 decitorr = 10^{-1} torrs.

The definition of a torr is as follows:

The torr is a non-SI unit of pressure, named after Evangelista Torricelli. Its symbol is Torr.

Metric conversions and more

ConvertUnits.com provides an online
conversion calculator for all types of measurement units.
You can find metric conversion tables for SI units, as well
as English units, currency, and other data. Type in unit
symbols, abbreviations, or full names for units of length,
area, mass, pressure, and other types. Examples include mm,
inch, 100 kg, US fluid ounce, 6'3", 10 stone 4, cubic cm,
metres squared, grams, moles, feet per second, and many more!