The pilot of the glider reported that prior to the accident flight, he had not flown in over 90 days. The purpose of the accident flight was to refamiliarize himself with the tasking area of an upcoming soaring contest, with a general aim to stay within gliding distance of the departure gliderport. For about 2 hours, the pilot flew south of the gliderport at altitudes between 3,000 to 4,000 ft above ground level. He then encountered weaker soaring conditions and miscalculated his altitude by 300 ft due to a discrepancy between the glider’s primary altimeter and the altitude displayed on his GPS/moving map computer. By that time, he was too low to glide back to the gliderport and elected to land in a field about 5 miles southeast of it. During the landing, the left wing struck a fence and sustained substantial damage. The pilot added that there were no preimpact mechanical malfunctions with the glider.