Absolute Efficiency refers to measures of engine performance gained by comparing an engine to an 'ideal' engine. The ideal engine has a nominated efficiency of 100%. The engine being compared typically has an efficiency of less than 100%.

A BUNO is the Bureau Number for an aircraft. Each record for a BUNO occurs at a given date and time.

A Calculated Performance Run is where an engine is tested in ideal circumstances to measure its performance against an 'ideal' engine. EngTrend does not use these measures in its calculations, but you can enter this information into any record and generate a Performance Graph that shows this data alongside the data produced by EngTrend.

Clipping is a display option in EngTrend which forces the data to be displayed within the range of the graph axes. Data which is outside the range of the graph axes is displayed as if it was **at** the limit. Clipping can be applied both vertically and horizontally.

The dateline is a vertical line that indicates the current record in a graph. When you have the Data Window open, the data for the record highlighted by the dateline is displayed.

Diagnosis (the process of using diagnostics) involves working through questions with specified possible answers, in order to determine a fault.

If Engine 1 is the reference engine then the Fuel Flow Line (FF Line) for Engine 2 is the graph of (PWR2 / FF2) / (PWR1 / FF1).

The graph of (PWR2 / FF2) / (PWR1 / FF1) is a relative efficiency measure of how efficient Engine 2 is at producing power per unit of fuel relative to Engine 1.

The reference engine is the engine against which all other engines are compared.

Relative Efficiency is the efficiency of one engine compared to another engine.

Smoothing is a statistical technique that can be applied to the graphs produced by EngTrend. It is like 'blunting' the accuracy of the measurements so as to produce a more generalized (and easier to read) graph. EngTrend smoothing involves 3, 5, 7 or 9 point averaging of the data.

A squadron is a collection of BUNOs. See BUNO.

The subsystem matrix is a table presenting the formulas used in EngTrend. It also presents the main engine components whose failures cause recognizable changes to the graphical output of EngTrend.

If Engine 1 is the reference engine then the Thermodynamic Line (Thermo Line) for Engine 2 is the graph of (TIT2 / FF2) / (TIT1 / FF1).

The graph of (TIT2 / FF2) / (TIT1 / FF1) is a relative efficiency measure of how efficient Engine 2 is at producing turbine temperature per unit of fuel relative to Engine 1.

If Engine 1 is the reference engine then the Turbine Inlet Temperature Line (TIT Line) for Engine 2 is the graph of (PWR2 / TIT2) / (PWR1 / TIT1).

The graph of (PWR2 / TIT2) / (PWR1 / TIT1) is a relative efficiency measure of how efficient Engine 2 is at producing power per unit of turbine inlet temperature relative to Engine 1.

A unitless measure is a ratio of two measures whose units are the same. As one is divided against the other, the units are cancelled. For example in EngTrend, the Fuel Flow line of Engine 2 to Engine 1 is (PWR2 / FF2) / (PWR1 / FF1). The numerator and denominator both have units (of power per rate of fuel flow), but when expressed as a ratio (which is what a relative measure is), the units are cancelled.