Is syaku an ancient Chinese unit of measurement (Suanfa tong zong)? According to multiple sources the following problem would be found in Suanfa tong zong (like on cut-the-knot)

Two reeds of equal height project 3 syaku above the surface of a pond.
If we draw the top of one reed 9 syaku in the direction of the shore
so that the top is just touching the surface of the water, find the
depth of the pond.

(Cut-the-knot claims the book contains the illustration, but another source claims the illustration is Japanese)
Anyhow: I assume Syaku would be an ancient Chinese unit of measurement. But I couldn't retrieve any information on this unit. How is it defined, how much would 1 syaku be in modern units of measurement?
I tried digging up the original problem, but when searching for the original (or any later reprints) I get stuck on the Chinese symbols. Could anyone help me out?
Not sure if &quot;Chinese Language&quot; is the right place for this question. I've been thinking about or &quot;History of Science and Mathematics&quot;, but I think the probability of someone owning &quot;Suanfa tong zong&quot; would be the greatest here (?)
I believe this is the original text:

今有葭二莖生池中，並根杪齊，出水三尺，即葭一莖斜去至岸九尺，與水適平，問水深若干？

It also comes with the following, hard to read, illustration:




This is the measure word you're asking about:
尺
MDBG:

chǐ
a Chinese foot / one-third of a meter / a ruler / a tape-measure / one of the three acupoints for measuring pulse in Chinese medicine / CL: 支, 把

Wiktionary

1 chi; Chinese foot (a traditional Chinese unit of distance based on the human forearm and equal to 10 cun (寸) or 1/10 zhang (丈))
2 (Mainland China) mainland chi; Chinese foot, standardized in 1984 as 1/3 meter
3 (Taiwan) Taiwanese foot, standardized as 10/33 meter and identical to the Japanese shaku
4 (Hong Kong) chek; Hong Kong foot, standardized as 0.371475 meters
5 (informal) imperial foot
6 ruler (straightedge) (Classifier: 把)
7 tape measure

Japanese Shaku is also:

10/33 meter