thumb on the scale是什么意思

putting her thumb on the scale-->直译是「把姆指放在磅秤上」，意思是借力影响结果。 (转自香港某网站)

拇指上的规模,有这样一个报道

If someone puts their thumb on the scale when weighing something, it makes it look heavier than it is, so a vendor might do this to cheat their customer.

此成语的原意指商人故意在秤物时将拇指按在秤上以增加重量，借以欺骗顾客。

Now a day, the meanings of the idiom are depicted as the following:
If you put your thumb on the scales, you try to influence the result of something in your favor.
put the thumb on the scale -- 以某种影响力来影响事情的结果，其结果是对当事人有利的。

'Thumb on the scale' shows it can affect the result.

e.g. "Does income act as 'thumb on the scale'? The evidence analyzed here suggests that it does, and that the disadvantage to lower-income students is more pronounced than some prominent higher education observers claim."
薪资所得是否有很大的影响力？ 。。。。

Hope this helps.

Cheers

Note: 本人已在海外生活了数十载。为了慎重起见，我的答案都与老美或老英交换过意见，你放心使用