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Frequently asked questions

• [Proudman Oceanogaphic Laboratory FAQs]
• [Permanent Service for Mean Sea Level FAQs]

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Tide clocks

Most tide clocks work by using a 12 hour 25 minute cycle. Generally in the UK and Ireland they would vary in accuracy between plus or minus 30 minutes over a 30 day period. Therefore it is necessary to reset them using local tide tables every month or so.

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Tidal/tide watches

Some watches with a moon/tide mode require lunitidal intervals for predicting high and low waters.

High water lunitidal interval
The high water lunitidal interval (or high water interval) is the time interval between the moon's transit and the next high water. The interval may be taken from the local time of moon's transit to the local time of high water, or it may be taken from the Greenwich time of the moon's transit to the standard time of high water.

Mean high water interval
The mean high water interval is the mean value of all the high water intervals throughout at least a lunation of 29 days.

Use the table below to set the moon/tide mode of your watch
Mean lunitidal intervals (mean high water intervals) have been calculated using

Interval (hrs) = M₂ phase (degrees) x M₂ period (hrs) / 360 (degrees)

These values should be sufficient information for watches that use the lunitidal interval to indicate high and low waters. (List below ordered by latitude.)

Please note:
If your UK location is not mentioned try using the nearest one or average between the two nearest ports on either side.
This is not guaranteed to work. Check your watch against local tide tables to confirm your setting.

Port/Location	Latitude	Longtiude	Interval (hrs : mins)
ST. HELIER	49° 11'N	2° 7'W	6:18
ST. MARY'S	49° 55'N	6° 19'W	4:31
NEWLYN	50° 6'N	5° 33'W	4:36
FALMOUTH	50° 9'N	5° 3'W	5:02
PLYMOUTH (DEVONPORT)	50° 22'N	4° 11'W	5:18
NEWQUAY	50° 25'N	5° 5'W	4:53
TORQUAY	50° 28'N	3° 31'W	5:51
PORTLAND	50° 34'N	2° 26'W	6:40
WEYMOUTH	50° 36'N	2° 27'W	6:36
BOURNEMOUTH	50° 43'N	1° 52'W	9:24
CHRISTCHURCH (QUAY)	50° 44'N	1° 46'W	10:37
LYMINGTON ENTRANCE	50° 44'N	1° 30'W	11:02
ISLE OF WIGHT - COWES	50° 46'N	1° 18'W	11:21
NEWHAVEN	50° 47'N	0° 3'E	11:05
PORTSMOUTH	50° 48'N	1° 7'W	11:16
LITTLEHAMPTON	50° 48'N	0° 32'W	11:08
SHOREHAM	50° 50'N	0° 15'W	11:06
DUNGENESS	50° 54'N	0° 58'E	11:14
SOUTHAMPTON	50° 54'N	1° 24'W	11:19
DOVER	51° 7'N	1° 19'E	11:27
ILFRACOMBE	51° 13'N	4° 7'W	5:36
HINKLEY POINT	51° 13'N	3° 8'W	6:19
MINEHEAD	51° 13'N	3° 28'W	6:11
MARGATE	51° 24'N	1° 23'E	11:47
SHEERNESS	51° 27'N	0° 45'E	12:12
TILBURY	51° 27'N	0° 22'E	0:18
NORTH WOOLWICH	51° 30'N	0° 5'E	0:44
SHIVERING SANDS	51° 30'N	1° 5'E	11:59
LONDON BRIDGE	51° 30'N	0° 5'W	1:10
AVONMOUTH	51° 31'N	2° 43'W	6:57
SOUTHEND	51° 31'N	0° 43'E	12:11
CORYTON	51° 32'N	0° 31'E	12:24
NEWPORT	51° 33'N	2° 59'W	6:44
MUMBLES	51° 34'N	3° 59'W	5:57
SWANSEA	51° 37'N	3° 55'W	5:57
MILFORD HAVEN	51° 42'N	5° 3'W	5:58
RINGASKIDDY	51° 50'N	8° 19'W	5:15
COBH	51° 50'N	8° 18'W	5:09
WALTON-ON-THE-NAZE	51° 51'N	1° 16'E	11:25
CORK CITY	51° 54'N	8° 27'W	4:15
HARWICH	51° 57'N	1° 17'E	11:18
MISTLEY QUAY	51° 57'N	1° 5'E	11:30
FELIXSTOWE	51° 57'N	1° 21'E	11:05
FISHGUARD	52° 1'N	4° 59'W	7:09
ROSSLARE HARBOUR	52° 15'N	6° 21'W	5:25
BARROW BRIDGE	52° 16'N	7° 0'W	5:25
ABERYSTWYTH	52° 25'N	4° 6'W	7:55
LOWESTOFT	52° 28'N	1° 45'E	8:57
GORLESTON	52° 34'N	1° 44'E	8:17
RIVER SHANNON TARBERT ISLAND	52° 35'N	9° 22'W	5:17
BARMOUTH	52° 43'N	4° 3'W	8:14
KING'S LYNN	52° 45'N	0° 24'E	6:34
WEST LIGHTHOUSE	52° 49'N	0° 13'E	6:17
WEST STONES	52° 49'N	0° 21'E	6:19
ROARING MIDDLE (WASH)	52° 55'N	0° 18'E	6:04
TABS HEAD	52° 56'N	0° 5'E	6:13
HUNSTANTON	52° 56'N	0° 29'E	6:11
CROMER	52° 56'N	1° 18'E	6:29
GIBRALTAR POINT	53° 5'N	0° 20'E	5:54
SKEGNESS	53° 9'N	0° 21'E	5:47
GALWAY	53° 16'N	9° 3'W	4:50
BOYGRIFT	53° 18'N	0° 18'E	5:38
EASTHAM	53° 19'N	2° 57'W	11:22
HOLYHEAD	53° 19'N	4° 37'W	10:04
INNER DOWSING (WASH)	53° 19'N	0° 35'E	5:35
LLANDUDNO	53° 20'N	3° 49'W	10:41
DUBLIN (NORTH WALL)	53° 21'N	6° 13'W	11:16
HILBRE ISLAND	53° 23'N	3° 13'W	10:57
BIRKENHEAD (ALFRED LOCK)	53° 24'N	3° 1'W	11:09
LIVERPOOL (PRINCES PIER)	53° 25'N	3° 0'W	11:09
LIVERPOOL (GLADSTONE LOCK)	53° 27'N	3° 1'W	11:04
BULL SAND FORT	53° 33'N	0° 4'E	5:16
SPURN POINT	53° 35'N	0° 7'E	5:12
IMMINGHAM	53° 38'N	0° 11'W	5:35
BLACKTOFT	53° 41'N	0° 42'W	6:58
HULL	53° 44'N	0° 21'W	5:59
WITHERNSEA	53° 44'N	0° 2'E	4:37
FLEETWOOD	53° 55'N	3° 0'W	11:15
HEYSHAM	54° 2'N	2° 55'W	11:14
HALFWAY SHOALS	54° 2'N	3° 12'W	11:11
ROA ISLAND	54° 4'N	3° 10'W	11:20
PORT ERIN	54° 5'N	4° 46'W	11:05
BARROW (RAMSDEN DOCK)	54° 6'N	3° 13'W	11:24
DOUGLAS	54° 9'N	4° 28'W	11:16
SCARBOROUGH	54° 17'N	0° 23'W	3:49
WHITBY	54° 29'N	0° 37'W	3:35
BELFAST	54° 36'N	5° 55'W	10:54
RIVER TEES ENTRANCE	54° 38'N	1° 9'W	3:18
WORKINGTON	54° 39'N	3° 34'W	11:27
BANGOR (N.IRELAND)	54° 40'N	5° 40'W	10:57
PORTPATRICK	54° 51'N	5° 7'W	11:27
LARNE	54° 51'N	5° 47'W	10:55
RIVER TYNE (NORTH SHIELDS)	55° 0'N	1° 26'W	3:04
LONDONDERRY	55° 0'N	7° 19'W	8:10
COLERAINE	55° 10'N	6° 46'W	6:50
PORTRUSH	55° 12'N	6° 40'W	6:47
MALIN HEAD	55° 18'N	7° 15'W	6:07
ISLAY (PORT ELLEN)	55° 38'N	6° 11'W	3:07
MILLPORT	55° 45'N	4° 54'W	11:49
GREENOCK	55° 58'N	4° 49'W	11:55
LEITH	55° 59'N	3° 11'W	1:54
ROSYTH	56° 1'N	3° 27'W	1:53
OBAN	56° 25'N	5° 29'W	5:38
TOBERMORY	56° 37'N	6° 4'W	5:49
ABERDEEN	57° 9'N	2° 4'W	0:50
MORAY FIRTH	57° 36'N	4° 0'W	11:37
CROMARTY FIRTH	57° 41'N	4° 1'W	11:33
ULLAPOOL	57° 54'N	5° 9'W	6:55
STORNOWAY	58° 12'N	6° 23'W	6:49
WICK	58° 26'N	3° 5'W	11:07
KINLOCHBERVIE	58° 27'N	5° 3'W	7:10
LERWICK	60° 9'N	1° 8'W	10:45
SULLOM VOE	60° 27'N	1° 18'W	9:13