For his whole working life Jensen was an amateur mathematician only doing mathematics in his spare time. However, he reached a very high level of expertise as a mathematician as he did as a telephone engineer.
Para sa kanyang trabaho buong buhay Jensen ay isang apisyonado dalubbilang lamang sa paggawa ng matematika sa kanyang ekstrang oras. Gayunman, siya umabot ng isang mataas na antas ng kadalubhasaan bilang isang dalub-agbilang bilang siya ay bilang ng telepono ng isang engineer.