The Urgency of Developing a Conservation of Weight Instrument to Measure Mathematics Learning Readiness in Weight Measurement for Phase B Elementary School Students Hana Uswatun Hasanah, Karlimah Karlimah, Tb Moh Irma Ari Irawan Jurnal Pendidikan Matematika Vol. 17 No. 2 2026 DOI 10.36709/jpm.v17i2.370