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Triangulation Pillar S4004: Frog Firle 
Location
Grid reference: TQ 50879 01072.
Landranger 199: Eastbourne & Hastings, Battle & Heathfield.
Waypoint: TP0430.
Neighbouring Triangulation Pillars
| S3975 | The Comp 1.35km to the west. |
| S4268 | Chyngton 2.03km to the south. |
| S3977 | Southlands 2.50km to the west. |
| S4042 | Denton Hill 3.19km to the northwest. |
| 11114 | Seaford Head 3.58km to the southwest. |
Third Geodetic Levelling, England & Wales (1950-68)
This triangulation pillar was used during the Third geodetic levelling, England & Wales. It was included on the Croydon to Alfriston and Guestling to Alfriston levelling lines.