If conducted accurately, identical investigations should produce similar results. Sometimes, errors, like measurement errors, can cause differences in results.

Sandra and Jeremy are neighbors who tested different brands of seeds in their gardens for six weeks. They grew identical gardens in their yards and recorded results. Each of them tried three brands of pea plant seeds and recorded the plants' heights at the end of each week. They discovered Jeremy's plants were much taller on average than Sandra's plants every week.

Which statement describes a measurement error that may have caused such a significant difference in their results?