one chart

[Robo]

The last two or three test I have taken, the tester on does one chart is that good or bad

[George W. Maschke]

Standard practice is for the polygrapher to collect more than one chart.

[beech trees]

Standard practice is for the polygrapher to collect more than one chart.

Indeed, many polygraph associations stipulate as much in their bylaws and rules of conduct. One example, from the Virginia Polygraphers Association:

§ 3.14. Chart analysis.

An examiner shall not render a verbal or written report based upon polygraph test chart analysis without having conducted at least two polygraph tests. Each relevant question must have been asked at least once on each of at least two polygraph tests.

Although I doubt any polygrapher's association would actually sanction one of their own, one could at least complain should the polygrapher fail to employ even the most basic professional conduct.