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复测固定角规点时，令保留木和进界木的期初断面积分别为ｇ１和ｇ０，它们的期末断面积为ｇ２，若把断面积比（ｇ１／ｇ２）和（ｇ０／ｇ２）分别称为保留木和进界木期初断面积特征值δ１和δ０，而它们的期末特征值仍为δ＝１，则林分每公顷断面积生长量△Ｇ＝Ｆ（∑Ｚ２ｉ＝１δｉ－∑Ｚ１ｊ＝１δ１ｊ－∑Ｚ２－Ｚ１ｋ＝１δｏｋ）。当保留木和进界木的期初形高分别为ｈｆ１和ｈｆ０，它们的期末形高为ｈｆ２时，则林分每公顷的蓄积生长量△Ｍ＝Ｆ（∑Ｚ２ｉ＝１ｈｆ２ｉ－∑Ｚ１ｊ＝１（δ１ｈｆ１）ｊ－∑Ｚ２－Ｚ１ｋ＝１（δ０ｈｆ０）ｋ。期初特征值法的特点是，既能保持直接法的优点———与林分蓄积现状具有一致性，便于连续清查，又能避免其缺点———抽样效率低。能真实地反映林分生长的连续性、渐进性。模拟实验证明，期初特征值法的抽样精度为９５％左右，平均系统误差为±５％左右。抽样效率是直接法的１０—３０倍。
When revising the fixed angle gauge, let the initial cross-sectional areas of the wood and the ingrowth wood be g1 and g0, respectively, and their end-of-period cross-sectional area is g2. If the sectional area ratios (g1 / g2) and (g0 / g2) Is called reserved wood and the beginning of the woodpectrum initial area characteristic values δ1 and δ0, and their end of the eigenvalue is still δ = 1, the forest per hectare area growth △ G = F (ΣZ2i = 1δi-ΣZ1j = 1δ1j-ΣZ2-Z1k = 1δok). When the initial shape of the preserved wood and the entrance wood is hf1 and hf0, respectively, and their final height is hf2, the accumulated volume of growth per hectare ΔM = F (ΣZ2i = 1hf2i-ΣZ1j = 1 ( δ1hf1) j-ΣZ2-Z1k = 1 (δ0hf0) k. The characteristic of the initial eigenvalue method is that it not only maintains the advantages of the direct method-it is consistent with the status of the stand volume accumulation, Disadvantages --- low sampling efficiency can truly reflect the continuity of forest growth, gradual. Simulation results show that the initial eigenvalue sampling accuracy of about 95%, the average system error of ± 5%. Sampling efficiency is Direct method 10-30 times.