diff --git a/src/lib/sudoku-model.js b/src/lib/sudoku-model.js
index 277eee9..f4175d5 100644
--- a/src/lib/sudoku-model.js
+++ b/src/lib/sudoku-model.js
@@ -57,6 +57,7 @@ const difficultyLevels = [
 ];
 
 const MAX_SAVED_PUZZLES = 5;
+const ALL_CANDIDATES_SUM = 1022;
 
 const emptySet = Set();
 const charCodeOne = '1'.charCodeAt(0);
@@ -951,7 +952,37 @@ export const modelHelpers = {
         return grid.set('modalState', {
             modalType: MODAL_TYPE_SOLVER,
             initialDigits: grid.get('initialDigits'),
-            allDigits: grid.get('cells').map(c => c.get('digit')).join(''),
+            allDigits: grid.get('cells')
+                .map(c => {
+                    const encode_as_str = (encoded_cell) => {
+                        let encoded_str = encoded_cell.toString(32);
+                        if (encoded_str.length < 2) {
+                            encoded_str = '0' + encoded_str;
+                        }
+                        return encoded_str;
+                    };
+                    
+                    const digit = parseInt(c.get('digit'));
+                    if (c.get('isGiven')) {
+                        // increment to set 'clue' flag
+                        const encoded_cell = Math.pow(2, digit) + 1;
+                        return encode_as_str(encoded_cell);
+                    }
+                 
+                    // cell based on user input
+                    if (digit === 0) {
+                        const candidates = c.get('innerPencils').toArray();
+                        const encoded_cell = candidates.length !== 0
+                            ? candidates.map(c => Math.pow(2, parseInt(c)))
+                                .reduce((a, b) => a + b, 0)
+                            : ALL_CANDIDATES_SUM;
+                        return encode_as_str(encoded_cell);
+                    } else {
+                        // return digit as is
+                        const encoded_cell = Math.pow(2, digit);
+                        return encode_as_str(encoded_cell);
+                    }
+                }).join(''),
             passProgressSetting,
             escapeAction: 'close',
         });
diff --git a/src/lib/sudoku-model.test.js b/src/lib/sudoku-model.test.js
index ca77e1a..3c3a1a5 100644
--- a/src/lib/sudoku-model.test.js
+++ b/src/lib/sudoku-model.test.js
@@ -1039,3 +1039,100 @@ test('check digits', () => {
         },
     });
 });
+
+test('check modal solver', () => {
+    let grid = newSudokuModel({initialDigits: initialDigitsComplete, skipCheck: true});
+    let result = modelHelpers.showSolverModal(grid).get('modalState');
+    expect(result['allDigits']).toBe(
+        'vuvuvuvuvu030509vu' +
+        '030509vuvu81vu0hvu' +
+        '81vu0hvuvu412111vu' +
+        '412111vuvuvuvuvuvu' +
+        'vuvuvuvuvuvuvuvuvu' +
+        'vuvuvuvuvuvu030509' +
+        'vu030509vuvu81vu0h' +
+        'vu81vu0hvuvu412111' +
+        'vu412111vuvuvuvuvu'
+    );
+
+    grid = modelHelpers.showCalculatedCandidates(grid);
+    expect(grid.get('currentSnapshot')).toBe(
+        '11N569,12N59,13N79,14N69,15N4569,19N789,' +
+        '24N69,25N569,27N9,29N79,' +
+        '32N9,34N29,35N239,39N19,' +
+        '44N1289,45N123489,46N2349,47N49,48N89,49N89,' +
+        '51N2349,52N349,53N189,54N126789,55N123456789,56N234569,57N459,58N789,59N6789,' +
+        '61N49,62N49,63N89,64N6789,65N456789,66N4569,' +
+        '71N59,75N679,76N69,78N9,' +
+        '81N39,83N9,85N129,86N29,' +
+        '91N349,95N1289,96N29,97N39,98N19,99N129'
+    );
+    result = modelHelpers.showSolverModal(grid).get('modalState');
+    expect(result['allDigits']).toBe(
+        'j0h0k0i0jg030509s0' +
+        '030509i0j081g00hk0' +
+        '81g00hg4gc412111g2' +
+        '412111o6ougsggo0o0' +
+        'gsgoo2u6vujshgs0u0' +
+        'ggggo0u0vgjg030509' +
+        'h0030509m0i081g00h' +
+        'g881g00hg6g4412111' +
+        'go412111o6g4g8g2g6'
+    );
+    
+    grid = modelHelpers.applySelectionOp(grid, 'setSelection', 72);
+    grid = modelHelpers.updateSelectedCells(grid, 'setDigit', 4);
+    grid = modelHelpers.applySelectionOp(grid, 'setSelection', 34);
+    grid = modelHelpers.updateSelectedCells(grid, 'setDigit', 8);
+    expect(grid.get('currentSnapshot')).toBe(
+        '11N569,12N59,13N79,14N69,15N4569,19N789,' +
+        '24N69,25N569,27N9,29N79,' +
+        '32N9,34N29,35N239,39N19,' +
+        '44N129,45N12349,46N2349,47N49,48D8,49N9,' +
+        '51N239,52N349,53N189,54N126789,55N123456789,56N234569,57N459,58N79,59N679,' +
+        '61N9,62N49,63N89,64N6789,65N456789,66N4569,' +
+        '71N59,75N679,76N69,78N9,' +
+        '81N39,83N9,85N129,86N29,' +
+        '91D4,95N1289,96N29,97N39,98N19,99N129'
+    );
+    result = modelHelpers.showSolverModal(grid).get('modalState');
+    expect(result['allDigits']).toBe(
+        'j0h0k0i0jg030509s0' +
+        '030509i0j081g00hk0' +
+        '81g00hg4gc412111g2' +
+        '412111g6gugsgg80g0' +
+        'gcgoo2u6vujshgk0m0' +
+        'g0ggo0u0vgjg030509' +
+        'h0030509m0i081g00h' +
+        'g881g00hg6g4412111' +
+        '0g412111o6g4g8g2g6'
+    );
+
+    grid = modelHelpers.applySelectionOp(grid, 'setSelection', 13);
+    grid = modelHelpers.updateSelectedCells(grid, 'clearCell');
+    grid = modelHelpers.applySelectionOp(grid, 'setSelection', 50);
+    grid = modelHelpers.updateSelectedCells(grid, 'clearCell');
+    expect(grid.get('currentSnapshot')).toBe(
+        '11N569,12N59,13N79,14N69,15N4569,19N789,' +
+        '24N69,27N9,29N79,' +
+        '32N9,34N29,35N239,39N19,' +
+        '44N129,45N12349,46N2349,47N49,48D8,49N9,' +
+        '51N239,52N349,53N189,54N126789,55N123456789,56N234569,57N459,58N79,59N679,' +
+        '61N9,62N49,63N89,64N6789,65N456789,' +
+        '71N59,75N679,76N69,78N9,' +
+        '81N39,83N9,85N129,86N29,' +
+        '91D4,95N1289,96N29,97N39,98N19,99N129'
+    );
+    result = modelHelpers.showSolverModal(grid).get('modalState');
+    expect(result['allDigits']).toBe(
+        'j0h0k0i0jg030509s0' +
+        '030509i0vu81g00hk0' +
+        '81g00hg4gc412111g2' +
+        '412111g6gugsgg80g0' +
+        'gcgoo2u6vujshgk0m0' +
+        'g0ggo0u0vgvu030509' +
+        'h0030509m0i081g00h' +
+        'g881g00hg6g4412111' +
+        '0g412111o6g4g8g2g6'
+    );
+});