Use the plastic-card method; or measure and enter the length of the blue ruler in Settings▸General (in millimeters). This is automatically saved and needs only to be repeated when changing screens or resolution.

Important: After calibration, don’t change the zoom level of your operating system or the browser! (Or recalibrate) Best re-check with the plastic card – easy and fast.

Enter in Settings▸General (in centimeters, there’s a conversion to inches). It must be large enough to avoid ceiling effects (see Manual entry): “max possible acuity” ≙ “min possible LogMAR” must be better than your desired best acuity. The setting is automatically saved.

DIN and ISO norms prescribe the range 80–320 cd/m² (recommended: 200 cd/m²). This is easy to achieve with current display units; most cases: set to near maximum, keeping black black.

The room should not be dark¹. No light sources or reflective surfaces seen by the testee should be brighter than the visual display unit. Additionally, glare sources such as spotlights, light reflections, or very bright surfaces should not be within the testee’s field of view. Surprisingly, the standards and norms do not specify particular values for the surround. An illumination of 10–300 lx seems good to me.

¹Darkening the room is not good for acuity assessment, but for refraction: With larger pupils, any ametropias have a stronger effect.

• For acuity: not very important. Ignore, or go to SettingsGamma and use the ± buttons as explained there.
• For Vernier: semi-important. Perform the simple calibration above.
• For contrast thresholds: very important. Best use a screen calibrator (these have become very affordable, e.g. Datacolor’s Spyder [must be the “Elite” or better if gamma 1.0 desired]), then …
  • either use the screen calibrator to measure current gamma, or set to your preferred gamma value (e.g. 2.0). Then enter this value in FrACT’s gamma textbox.
  • or calibrate the screen to a gamma=1.0, and enter that gamma value of 1.0 in Settings▸Gamma.
• This setting is automatically saved.

• This is incredibly useful!
• If you are using a remote keypad for response entry, make sure it is oriented correctly :). Really.

This avoids unwanted responses, caused by prolonged pressing of a key. Use your operating system’s keyboard options to do this.

Running a binocular training run with your participants has proven useful. They can familiarise themselves with the test, and you can explain the “forced choice” situation, e.g.: “use your best guess, even if you don’t see it!” Usually, I don’t even analyse the results of this run.

• Select the correct decimal mark (comma or period) for your locality in Settings▸General, bottom left. (Important: otherwise the spreadsheet might interpret your results as dates!). In FrACT₁₀ the default is “automatic”, that could be sufficient.
• Decide whether you only want the final result or the full history (with reaction times etc.) and select in Settings▸General.
• Start the spreadsheet program (e.g. Excel, LibreOffice, or Numbers) beforehand, add additional information you might want, and switch between FrACT and spreadsheet with the task-switcher shortcut (⌘-tab for Macs, alt-tab for Windows).
• After each test run, switch to the spreadsheet and paste. Voilà!

More export options in the FrACT₁₀ Manual.

When the subject reports “whoops, pressed the wrong key” during the first 3 trials: It’s best to abort by pressing “5” twice and restart this run.

Much more detail here: FrACT₁₀ Manual or FrACT_classic Manual [PDF].