Digit Focus

Digit focus is a filtering system that highlights cells containing specific digits — either as placed values or as candidates. Use it to spot patterns, track eliminations, and analyse the grid.

Quick Start

Enter digit focus mode in any of these ways:

  1. Tap the focus button on the toolbar
  2. Long-press a digit on the keypad (if enabled in Input Settings)
  3. Multi-finger tap (if configured to "Toggle Digit Focus")
  4. Via the Radial Menu (Focus category)

In focus mode, tap digits on the keypad to build your filter. Tap the focus button again (or use the exit button) to leave.

Note: Without persistent overlay (Pro), long-tap and radial menu actions enter focus mode. With persistent overlay, they toggle digit filters while staying in play mode.

Digit Filters

In focus mode, tap digits on the keypad to select multiple filters simultaneously. All cells containing any selected digit as a candidate are highlighted.

Multi-digit filter modes control how multiple selections combine. Access these via the Radial Menu:

For example, selecting digits 3 and 7 in 2+ mode highlights only cells that contain both 3 and 7 as candidates — useful for finding naked pairs and other patterns.

Special Filters

Beyond digit-based filters, focus mode offers cell-count filters. Toggle them from the focus mode toolbar or via the Radial Menu:

These are particularly useful for spotting XY-Wings, XYZ-Wings, and other bent-set patterns.

Persistent Overlay (Pro Feature)

With a Pro subscription, you can pin the digit focus overlay and continue working — select cells, edit notes, place values — while the filter remains visible. Toggle the pin from the status bar.

Without Pro, you build your filter in focus mode, then switch back to play mode to edit the grid — the overlay disappears when you leave focus mode.

This is designed so that Pro users enjoy a seamless workflow, while free users can still access all the same analytical tools.

Focus in Projected Spaces

Digit focus works across all four Berthier spaces. When you switch to a projected space (rn, cn, or bn), focus adapts to the new coordinate system.

How Highlighting Changes

In rc-space, selecting a digit highlights cells containing that digit as a candidate. In projected spaces, the same selection highlights the corresponding axis:

Strong Links in Projected Spaces

Strong links (conjugate pairs) are available in projected spaces. When a candidate appears in exactly two unsolved cells within a row or column of the projected grid, a strong link connects them.

For example, in rn-space: if digit 5 can only go in columns 2 and 7 of row 3, a strong link appears between cells R3D5/C2 and R3D5/C7. This is the bilocation "digit 5 has exactly 2 possible columns in row 3", rendered as a visible connection.

To display strong links in a projected space:

  1. Switch to the desired space (rn, cn, or bn)
  2. Enter focus mode and switch to the Links submode
  3. Select a digit — strong links appear for that digit's conjugate pairs

Bi-value Filter as Bilocation Finder

The bi-value filter gains a new meaning in projected spaces. A cell with exactly 2 candidates in rn-space means "this digit has exactly 2 possible columns in this row" — a bilocation. Enabling the bi-value filter in a projected space therefore highlights all bilocations, which are the building blocks of fish patterns.

Tips

  1. Cycle with swipes — In play mode, horizontal swipes on the keypad cycle digit focus to the next/previous unsolved digit
  2. Combine digits — In focus mode, tap multiple digits on the keypad to find cells where they intersect
  3. Use bi-value filter — Quickly spot cells with exactly 2 candidates for XY-Chain patterns
  4. Multi-finger toggle — Configure a 3-finger tap to toggle focus mode without reaching for the toolbar

Related Features