Congratulations! Don’t hesitate to alert me: bach@uni-freiburg.de or open an issue on GitHub. Will fix ASAP.

Congratulations! Contact me: bach@uni-freiburg.de and we’ll see. Has worked before ;)

Short version: Nothing but implementation details.

Long version: Development of FrACT goes back to 1984; the dynamics of computer technology and specifically of web browsers enabled to go more and more on-line, culminating in FrACT₁₀ around 2020. Now FrACT₁₀ has every feature of the “classic” FrACT, and more. The basic algorithm (Best PEST) uses practically the same code base as three decades ago. Since FrACT₁₀ as a webApp can now be installed for off-line use there is no reason to use “classic” FrACT.
Any new development (e.g. plastic card calibration, or noise embedding) is only available in FrACT₁₀.

1. Take a look at the Manual 😇
2. If that does not answer your question, don’t hesitate to email me: bach@uni-freiburg.de.

The best possible acuity is based on “smallest stroke = smallest landolt gap” being 1 pixel. However, antialiasing allows to present fractional pixels, and the smallest possible element size can be set at: Settings>Acuity>min. stroke [px]. The default value here is 0.5 px. Since max possible decimal acuity is based on 1 pixel (thus demanding good test properties, safe side), the result can be a better value. The note on display resolution… in the manual provides more detail.

Yes, but you need a visual display unit (VDU) with really tiny pixels. In the Manual there is a note on display resolution… on this, with examples of suitable VDUs. The accessible acuity range is given on the Settings at screen bottom right.

The technical limitations are screen size and distance. Going close and using a large screen can bring you into ultra-low vision range. Then the problem arises if the observer has sufficient vision. Here is a discussion on this. Also the accessible acuity range is given on the Settings screen at bottom right.

Very demanding, an expert field by itself; so just some thoughts:

• May need a very large screen
• Should run in ⛶Fullscr. (Fullscreen) mode to not waste screen estate
• If the low vision condition is congenital, Sloan letters will not work, so consider Landolt Cs (possibly with only 4 alternatives, even if that needs more trials)
• Consider setting Settings>Acuity>Starting LogMAR to a higher value than the default 1.0, e.g. 2.5, to avoid initial frustration
• Settings>Acuity>Margin for biggest optotype: Is ½ stroke width enough for you?
• When ceiling effects occur, namely the largest optotype not seen, the result will indicate this (details in the manual here)

Well, I admit it’s a bit hidden; there are some idiosyncrasies in FrACT₁₀, suggestions welcome…
In  Settings>Gratings>What to sweep  select  Spatial frequency, "Acuity".

Absolutely, you can do that. Use Settings>Display Transformation to compensate for the image mirroring/inversion. [BTW: surface mirrors are needed to avoid double images.]

Enter a negative value for the Weber contrast in Settings>Acuity>Optotype contrast, e.g. with the max– button.

A good question… and the answer is complex. First: it depends on the size (Diameter), defaulf 60’. Second: an optotype (be it letter, Landolt C, tumbling E…) does not have a spatial frequency, rather it is a mixture (I’ve calculated the spectrum but never published it).

I had hoped to have a setting for this. However, after extensive experiments with the Multi-Screen Window Placement API, I conclude that it is not possible to programmatically move to 2nd screen without user interaction. So use these simple solutions:

• If you’re using FrACT₁₀ in a browser, just move the browser window to the 2nd screen.
• If you’re using the FrACT₁₀ webApp, just move the window to the 2nd screen (and, depending on browser, it will even remember that after restart).
• Using the older stand-alone app? Update to webApp :).

When the window is on the second screen, you can use the ⤧ ︎Fullscr. button to go, well, fullscreen. Also note: Need to repeat size calibration (“plastic card / blue ruler”) on the 2nd screen – its pixel size probably is different.

So the plastic card fits vertically but not horizontally (or vice-versa)?

In that case the pixels on your VDU are not square. While modern VDUs all have square pixels, it can happen that the screen resolution is set to a value not compatible with square pixels. We want to avoid that anyway, because that will lead to blur. Look for “Display resolution” (or similar) and try alternate combinations.

I see two possible scenarios:

• The settings for screen calibration (Length of blue ruler) and Observer distance combine to a very large optotype, and you see only its empty center
• The Optotype eccentricity setting is too large, shifting the optotype off screen.

If nothing rings a bell, use Settings>Set all to defaults: Now you should something, and you can proceed to apply your preferences in Settings.

The version number will only increment when I make major changes or add a feature. In contrast, the release date is updated whenever anything changes. Find them both at the main screen, top left; or use the About button – there not only FrACT₁₀’s version date is given but also the versions of embedded frameworks. The export format has its own version scheme, the exported data set starts with the current version number; this allows your analysis software to easily deal with changes here.

Please include the version when citing FrACT. Thank you!