diff --git a/models/summary.go b/models/summary.go
index 4fed09b..d9a1e0f 100644
--- a/models/summary.go
+++ b/models/summary.go
@@ -13,6 +13,8 @@ const (
 	SummaryMachine  uint8 = 4
 )
 
+const UnknownSummaryKey = "unknown"
+
 type Summary struct {
 	ID               uint           `json:"-" gorm:"primary_key"`
 	UserID           string         `json:"user_id" gorm:"not null; index:idx_time_summary_user"`
@@ -45,3 +47,55 @@ type SummaryViewModel struct {
 	Success        string
 	ApiKey         string
 }
+
+/* Augments the summary in a way that at least one item is present for every type.
+If a summary has zero items for a given type, but one or more for any of the other types,
+the total summary duration can be derived from those and inserted as a dummy-item with key "unknown"
+for the missing type.
+For instance, the machine type was introduced post hoc. Accordingly, no "machine"-information is present in
+the data for old heartbeats and summaries. If a user has two years of data without machine information and
+one day with such, a "machine"-chart plotted from that data will reference a way smaller absolute total amount
+of time than the other ones.
+To avoid having to modify persisted data retrospectively, i.e. inserting a dummy SummaryItem for the new type,
+such is generated dynamically here, considering the "machine" for all old heartbeats "unknown".
+*/
+func (s *Summary) FillUnknown() {
+	types := []uint8{SummaryProject, SummaryLanguage, SummaryEditor, SummaryOS, SummaryMachine}
+	missingTypes := make([]uint8, 0)
+	typeItems := map[uint8]*[]*SummaryItem{
+		SummaryProject:  &s.Projects,
+		SummaryLanguage: &s.Languages,
+		SummaryEditor:   &s.Editors,
+		SummaryOS:       &s.OperatingSystems,
+		SummaryMachine:  &s.Machines,
+	}
+	var somePresentType uint8
+
+	for _, t := range types {
+		if len(*typeItems[t]) == 0 {
+			missingTypes = append(missingTypes, t)
+		} else {
+			somePresentType = t
+		}
+	}
+
+	// can't proceed if entire summary is empty
+	if len(missingTypes) == len(types) {
+		return
+	}
+
+	// calculate total duration from any of the present sets of items
+	var timeSum time.Duration
+	for _, item := range *typeItems[somePresentType] {
+		timeSum += item.Total
+	}
+
+	// construct dummy item for all missing types
+	for _, t := range missingTypes {
+		*typeItems[t] = append(*typeItems[t], &SummaryItem{
+			Type:  t,
+			Key:   UnknownSummaryKey,
+			Total: timeSum,
+		})
+	}
+}
diff --git a/services/summary.go b/services/summary.go
index a029f6e..574498f 100644
--- a/services/summary.go
+++ b/services/summary.go
@@ -103,6 +103,10 @@ func (srv *SummaryService) Construct(from, to time.Time, user *models.User, reco
 	if len(existingSummaries) > 0 {
 		realFrom = existingSummaries[0].FromTime
 		realTo = existingSummaries[len(existingSummaries)-1].ToTime
+
+		for _, summary := range existingSummaries {
+			summary.FillUnknown()
+		}
 	}
 	if len(heartbeats) > 0 {
 		t1, t2 := time.Time(heartbeats[0].Time), time.Time(heartbeats[len(heartbeats)-1].Time)
@@ -197,7 +201,7 @@ func (srv *SummaryService) aggregateBy(heartbeats []*models.Heartbeat, summaryTy
 		}
 
 		if key == "" {
-			key = "unknown"
+			key = models.UnknownSummaryKey
 		}
 
 		if aliasedKey, err := srv.AliasService.GetAliasOrDefault(user.ID, summaryType, key); err == nil {
diff --git a/static/assets/app.js b/static/assets/app.js
index e587b83..453d3ec 100644
--- a/static/assets/app.js
+++ b/static/assets/app.js
@@ -57,7 +57,7 @@ function draw() {
                 .map(p => {
                     return {
                         label: p.key,
-                        data: [parseInt(p.total)],
+                        data: [parseInt(p.total) / 60],
                         backgroundColor: getRandomColor(p.key)
                     }
                 })
@@ -68,6 +68,14 @@ function draw() {
             legend: {
                 display: false
             },
+            scales: {
+                xAxes: [{
+                    scaleLabel: {
+                        display: true,
+                        labelString: 'Minutes'
+                    }
+                }]
+            },
             maintainAspectRatio: false,
             onResize: onChartResize
         }
diff --git a/version.txt b/version.txt
index afa2b35..b9268da 100644
--- a/version.txt
+++ b/version.txt
@@ -1 +1 @@
-1.8.0
\ No newline at end of file
+1.8.1
\ No newline at end of file