HJs Boeken en Instrumenten is part of piLot Survey Services and is first and foremost a digital museum of survey instruments. Sometimes extra instruments are sold through Catawiki or Marktplaats.
The collection is maintained as part of education services as well as personal hobby. The instruments are kept in working condition where possible and used for research experiments using period specific instruments.
I started collecting books while still in Nautical College. When I started teaching I acquired some instruments to use during practical lectures and historical techniques. Around 2015 I acquired some more and then got bitten by the collecting bug.
As with most collectors, it took me a while to figure out in which direction my collection should head and now I collect mainly Wild Heerbrugg instruments (generally 'green' only), survey sextants and sextants that deviate from the standard pattern in either size (usually small) or material (wood, paper, plastic). Besides I have some instruments to show the general development of survey instruments to allow comparison with modern instruments.
This website also shows some clocks. These are a hobby of my wife who restores these and does a little bit of collecting. As they do not deviate to far from the other instruments, why not...
There is no stock of instruments etc, I only sell instruments that I no longer think should be in the collection or that are 'double'. You can ask whether an instrument is for sale but don't bother if you are not willing to pay me at least what the instrument has cost me. Auction catalogues and Ebay are a good starting point to figure out if you want to ask me what some of the instruments are worth. They generally do not come cheap...
If you have any questions regarding the instruments, please do not hesitate to contact me. If I know something I will try to inform you. I also welcome additional information about my own instruments; the research is never over...