量 is a tone-changing character. In 量度 (measure) it's liáng (rising tone, the verb 'to measure'). In 重量 (zhòngliàng, 'weight') it's liàng (falling tone, the noun 'quantity'). Picking the wrong tone here is a common slip even for advanced learners.
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More technical / formal than the everyday 测量 (cèliáng). You'll see 量度 in physics, engineering and philosophical contexts ('量度时间' = 'measure time').
