diff --git a/gui/demos/calendar.py b/gui/demos/calendar.py
index 01dba8f..872ef16 100644
--- a/gui/demos/calendar.py
+++ b/gui/demos/calendar.py
@@ -1,9 +1,7 @@
-# calendar.py Test Grid class.
+# calendar.py Test Grid class. Requires date.py.
 
 # Released under the MIT License (MIT). See LICENSE.
 # Copyright (c) 2023 Peter Hinch
-# As written requires a 240*320 pixel display, but could easily be reduced
-# with smaller fonts.
 
 # hardware_setup must be imported before other modules because of RAM use.
 import hardware_setup  # Create a display instance
@@ -16,67 +14,14 @@ from gui.core.writer import CWriter
 import gui.fonts.font10 as font
 import gui.fonts.font14 as font1
 from gui.core.colors import *
-
-from time import mktime, localtime
-SECS_PER_DAY = const(86400)
-
-class Date:
-
-    days = ('Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday')
-    months = ('January', 'February', 'March', 'April', 'May', 'June', 'July', 'August',
-              'September', 'October', 'November', 'December')
-
-    def __init__(self):
-        self.now()
-
-    def now(self):
-        lt = list(localtime())
-        lt[3] = 6  # Disambiguate midnight
-        self.cur = mktime(lt) // SECS_PER_DAY
-        self.update()
-
-    def update(self, lt=None):
-        if lt is not None:
-            lt[3] = 6
-            self.cur = mktime(lt) // SECS_PER_DAY
-        lt = localtime(self.cur * SECS_PER_DAY)
-        self.year = lt[0]
-        self.month = lt[1]
-        self.mday = lt[2]
-        self.wday = lt[6]
-        ml = self.mlen(self.month)
-        self.month_length = ml
-        self.wday1 = (self.wday - self.mday + 1) % 7  # Weekday of 1st of month
-        # Commented out code provides support for UK DST calculation
-        #wdayld = (self.wday1 + ml -1) % 7  # Weekday of last day of month
-        #self.mday_sun = ml - (wdayld + 1) % 7  # Day of month of last Sunday
-
-    def add_days(self, n):
-        self.cur += n
-        self.update()
-    
-    def add_months(self, n):  # Crude algorithm for small n
-        for _ in range(abs(n)):
-            self.cur += self.month_length if n > 0 else -self.mlen(self.month - 1)
-            self.update()
-
-    def add_years(self, n):
-        lt = list(localtime(self.cur * SECS_PER_DAY))
-        lt[0] += n
-        self.update(lt)
-
-    def mlen(self, month):
-        days = (31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)[month - 1]
-        year = self.year
-        return days if days else (28 if year % 4 else (29 if year % 100 else 28))
-    
+from .date import DateCal
 
 class BaseScreen(Screen):
 
     def __init__(self):
 
         super().__init__()
-        self.date = Date()
+        self.date = DateCal()
         wri = CWriter(ssd, font, GREEN, BLACK, False)
         wri1 = CWriter(ssd, font1, WHITE, BLACK, False)
         col = 2
@@ -87,28 +32,28 @@ class BaseScreen(Screen):
         self.lbl = Label(wri, row, col, text = (colwidth + 4) * cols, justify=Label.CENTRE)
         row = self.lbl.mrow
         self.grid = Grid(wri, row, col, colwidth, rows, cols, justify=Label.CENTRE)
-        for n, day in enumerate(Date.days):
+        for n, day in enumerate(DateCal.days):
             self.grid[[0, n]] = day[:3]
 
         row = self.grid.mrow + 4
         ht = 30
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="y-", callback=self.adjust, args=(self.date.add_years, -1))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="y-", callback=self.adjust, args=("y", -1))
         col = b.mcol + 2
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="y+", callback=self.adjust, args=(self.date.add_years, 1))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="y+", callback=self.adjust, args=("y", 1))
         col = b.mcol + 5
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="m-", callback=self.adjust, args=(self.date.add_months, -1))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="m-", callback=self.adjust, args=("m", -1))
         col = b.mcol + 2
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="m+", callback=self.adjust, args=(self.date.add_months, 1))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="m+", callback=self.adjust, args=("m", 1))
         col = b.mcol + 5
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="w-", callback=self.adjust, args=(self.date.add_days, -7))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="w-", callback=self.adjust, args=("d", -7))
         col = b.mcol + 2
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="w+", callback=self.adjust, args=(self.date.add_days, 7))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="w+", callback=self.adjust, args=("d", 7))
         col = b.mcol + 5
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="d-", callback=self.adjust, args=(self.date.add_days, -1))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="d-", callback=self.adjust, args=("d", -1))
         col = b.mcol + 2
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="d+", callback=self.adjust, args=(self.date.add_days, 1))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, text="d+", callback=self.adjust, args=("d", 1))
         col = b.mcol + 5
-        b = Button(wri, row, col, height=ht, shape=CIRCLE, fgcolor=BLUE, text="H", callback=self.adjust, args=(self.date.now,))
+        b = Button(wri, row, col, height=ht, shape=CIRCLE, fgcolor=BLUE, text="H", callback=self.adjust, args=("h",))
         #row = b.mrow + 10
         col = 2
         row = ssd.height - (wri1.height + 2)
@@ -117,33 +62,42 @@ class BaseScreen(Screen):
         CloseButton(wri)  # Quit the application
 
     def adjust(self, _, f, n=0):
-        f(n) if n else f()
+        d = self.date
+        if f == "y":
+            d.year += n
+        elif f == "m":
+            d.month += n
+        elif f == "d":
+            d.day += n
+        elif f =="h":
+            d.now()
         self.update()
 
     def update(self):
         def cell():
-            #d.clear()
             if cur.year == today.year and cur.month == today.month and mday == today.mday:  # Today
                 d["fgcolor"] = RED
             elif mday == cur.mday:  # Currency
                 d["fgcolor"] = YELLOW
+            elif mday in sundays:
+                d["fgcolor"] = BLUE
             else:
                 d["fgcolor"] = GREEN
             d["text"] = str(mday)
             self.grid[idx] = d
 
-        today = Date()
+        today = DateCal()
         cur = self.date  # Currency
-        self.lbl.value(f"{Date.months[cur.month - 1]} {cur.year}")
+        self.lbl.value(f"{DateCal.months[cur.month - 1]} {cur.year}")
         d = {}  # Args for Label.value
         wday = 0
+        wday_1 = cur.wday_n(1)  # Weekday of 1st of month
         mday = 1
         seek = True
-        for idx in range(7, self.grid.ncells):
-            self.grid[idx] = ""
+        sundays = cur.mday_list(6)
         for idx in range(7, self.grid.ncells):
             if seek:  # Find column for 1st of month
-                if wday < cur.wday1:
+                if wday < wday_1:
                     self.grid[idx] = ""
                     wday += 1
                 else:
@@ -154,14 +108,12 @@ class BaseScreen(Screen):
                     mday += 1
                 else:
                     self.grid[idx] = ""
-        idx = 7
+        idx = 7  # Where another row would be needed, roll over to top few cells.
         while mday <= cur.month_length:
             cell()
             idx += 1
             mday += 1
-        day = Date.days[today.wday]
-        month = Date.months[today.month - 1]
-        self.lblnow.value(f"{day} {today.mday} {month} {today.year}")
+        self.lblnow.value(f"{today.day_str} {today.mday} {today.month_str} {today.year}")
 
 
 def test():
diff --git a/gui/demos/date.py b/gui/demos/date.py
new file mode 100644
index 0000000..2601ee0
--- /dev/null
+++ b/gui/demos/date.py
@@ -0,0 +1,160 @@
+# date.py Minimal Date class for micropython
+
+# Released under the MIT License (MIT). See LICENSE.
+# Copyright (c) 2023 Peter Hinch
+
+from time import mktime, localtime
+
+_SECS_PER_DAY = const(86400)
+def leap(year):
+    return bool((not year % 4) ^ (not year % 100))
+
+class Date:
+
+    def __init__(self, lt=None):
+        self.now(lt)
+
+    def now(self, lt=None):
+        self._lt = list(localtime()) if lt is None else list(lt)
+        self._update()
+
+    def _update(self, ltmod=True):  # If ltmod is False ._cur has been changed
+        if ltmod:  # Otherwise ._lt has been modified
+            self._lt[3] = 6
+            self._cur = mktime(self._lt) // _SECS_PER_DAY
+        self._lt = list(localtime(self._cur * _SECS_PER_DAY))
+
+    def _mlen(self, d=bytearray((31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31))):
+        days = d[self._lt[1] - 1]
+        return days if days else (29 if leap(self._lt[0]) else 28)
+
+    @property
+    def year(self):
+        return self._lt[0]
+
+    @year.setter
+    def year(self, v):
+        if  self.mday == 29 and self.month == 2 and not leap(v):
+            self.mday = 28  # Ensure it doesn't skip a month
+        self._lt[0] = v
+        self._update()
+
+    @property
+    def month(self):
+        return self._lt[1]
+
+    # Can write d.month = 4 or d.month += 15
+    @month.setter
+    def month(self, v):
+        y, m = divmod(v - 1, 12)
+        self._lt[0] += y
+        self._lt[1] = m + 1
+        self._lt[2] = min(self._lt[2], self._mlen())
+        self._update()
+
+    @property
+    def mday(self):
+        return self._lt[2]
+
+    @mday.setter
+    def mday(self, v):
+        if not 0 < v <= self._mlen():
+            raise ValueError(f"mday {v} is out of range")
+        self._lt[2] = v
+        self._update()
+
+    @property
+    def day(self):  # Days since epoch.
+        return self._cur
+
+    @day.setter
+    def day(self, v):  # Usuge: d.day += 7 or date_1.day = d.day.
+        self._cur = v
+        self._update(False)  # Flag _cur change
+
+    # Read-only properties
+
+    @property
+    def wday(self):
+        return self._lt[6]
+
+    # Date comparisons
+
+    def __lt__(self, other):
+        return self.day < other.day
+
+    def __le__(self, other):
+        return self.day <= other.day
+
+    def __eq__(self, other):
+        return self.day == other.day
+
+    def __ne__(self, other):
+        return self.day != other.day
+
+    def __gt__(self, other):
+        return self.day > other.day
+
+    def __ge__(self, other):
+        return self.day >= other.day
+
+    def __str__(self):
+        return f"{self.year}/{self.month}/{self.mday}"
+
+
+class DateCal(Date):
+    days = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
+    months = (
+        "January",
+        "February",
+        "March",
+        "April",
+        "May",
+        "June",
+        "July",
+        "August",
+        "September",
+        "October",
+        "November",
+        "December",
+    )
+
+    def __init__(self, lt=None):
+        super().__init__(lt)
+
+    @property
+    def month_length(self):
+        return self._mlen()
+
+    @property
+    def day_str(self):
+        return self.days[self.wday]
+
+    @property
+    def month_str(self):
+        return self.months[self.month - 1]
+
+    def wday_n(self, mday=1):
+        return (self._lt[6] - self._lt[2] + mday) % 7
+
+    def mday_list(self, wday):
+        ml = self._mlen()  # 1 + ((wday - wday1) % 7)
+        d0 = 1 + ((wday - (self._lt[6] - self._lt[2] + 1)) % 7)
+        return [d for d in range(d0, ml + 1, 7)]
+
+    # Optional: return UK DST offset in hours. Can pass hr to ensure that time change occurs
+    # at 1am UTC otherwise it occurs on date change (0:0 UTC)
+    # offs is offset by month
+    def time_offset(self, hr=6, offs=bytearray((0, 0, 3, 1, 1, 1, 1, 1, 1, 10, 0, 0))):
+        ml = self._mlen()
+        wdayld = self.wday_n(ml)  # Weekday of last day of month
+        mday_sun = self.mday_list(6)[-1]  # Month day of last Sunday
+        m = offs[self._lt[1] - 1]
+        if m < 3:
+            return m  # Deduce time offset from month alone
+        return int(
+            ((self._lt[2] < mday_sun) or (self._lt[2] == mday_sun and hr <= 1)) ^ (m == 3)
+        )  # Months where offset changes
+
+    def __str__(self):
+        return f"{self.day_str} {self.mday} {self.month_str} {self.year}"