The Dual Computations box on the General Solver tab:

is used to control the level of dual computations performed by the solver.

The choices for this option are:

When the None option is selected, LINGO does not compute any dual and range information. This option yields the fastest solution times, but is suitable only if you don’t require any dual information. In fact, the Solver|Rangecommand will not execute when dual computations are turned off.

When the Prices option is selected, LINGO computes dual values, but not the ranges on the duals. When Prices & Ranges is selected, LINGO computes both dual prices and ranges.

When the Prices, Opt Only option is selected, LINGO computes dual values on the optimizable rows only—fixed rows simply receive a dual value of 0.  Ranges are also not computed under this option.  This can be a useful option if LINGO is spending a lot of time in the "Computing Duals…" phase of the solution process.  This phase is devoted to the computation of dual values on the fixed rows.

LINGO defaults to the Prices option (computing all the dual prices but not ranges.)