Most bathroom scales suck like this, even expensive ones. You know what doesn't suck? Shipping scales! Think about it, a shipping scale MUST be accurate for calculating postage. They're often cheaper and FAR more accurate, and it's consistent 99% of the time. Mine was $40 and is accurate down to the twentieth of a pound. It's the same size as a bathroom scale and has the option to be plugged in, too. I think it might have a 400lb. weight limit, not sure about that. Here are a couple options that look comparable.
Smart Weigh Digital Heavy Duty Shipping and Postal Scale with Durable Stainless Steel Large Platform, 440 lbs Capacity x 6 oz Readability , UPS USPS Post Office Postal Scale and Luggage Scale https://www.amazon.com/dp/B0153I0418/ref=cm_sw_r_cp_apa_i_9jugBb4F7GG66
WeighMax W-4830 Industrial Postal Scale 330lb https://www.amazon.com/dp/B001AKV422/ref=cm_sw_r_cp_apa_i_ZlugBbM7QGWZK